______________________________________________________________________

  14   Templates                                                  [temp]

  ______________________________________________________________________

1 A template defines a family of types or functions.
          template-declaration:
                  exportopt template < template-parameter-list > declaration
          template-parameter-list:
                  template-parameter
                  template-parameter-list , template-parameter
  The declaration in a template-declaration shall declare  or  define  a
  function  or a class, define a static data member of a class template,
  define a member function or a member class of  a  class  template,  or
  define a member template of a class.  A template-declaration is a dec­
  laration.  A template-declaration is also a definition if its declara­
  tion defines a function, a class, or a static data member.

2 A  template-declaration  can appear only as a namespace scope or class
  scope declaration.  In a function template declaration,  the  declara­
  tor-id  shall be a template-name (i.e., not a template-id).  [Note: in
  a class template declaration, if the declarator-id is  a  template-id,
  the  declaration  declares  a  class  template  partial specialization
  (_temp.class.spec_).  ]

3 In  a  template-declaration,  explicit  specialization,  or   explicit
  instantiation  the  init-declarator-list in the declaration shall con­
  tain at most one declarator.  When  such  a  declaration  is  used  to
  declare a class, no declarator is permitted.

4 A  template  name may have linkage (_basic.link_).  A template, a tem­
  plate explicit specialization (_temp.expl.spec_), or a class  template
  partial  specialization  shall  not have C linkage.  If the linkage of
  one of these is something other than C or C++, the behavior is  imple­
  mentation-defined.  Template definitions shall obey the one definition
  rule (_basic.def.odr_).

5 The name of a class template shall not be declared  to  refer  to  any
  other  template,  class,  function,  object,  enumeration, enumerator,
  namespace, or type in the same scope (_basic.scope_).  Except  that  a
  function template can be overloaded either by (non-template) functions
  with the same name or by other function templates with the  same  name
  (_temp.over_),  a  template  name declared in namespace scope shall be
  unique in that namespace.

6 A non-inline template function or a static  data  member  template  is
  called  an exported template if its definition is preceded by the key­
  word export or if it has been previously declared  using  the  keyword

  export  in  the  same  translation  unit.   Declaring a class template
  exported is equivalent to declaring all  of  its  non-inline  function
  members,  static  data  members, member classes, and non-inline member
  templates which are defined in that translation unit exported.

7 Templates defined in an unnamed namespace shall not  be  exported.   A
  template  shall be exported only once in a program.  An implementation
  is not required to diagnose a violation of this rule.  A  non-exported
  template that is neither explicitly specialized nor explicitly instan­
  tiated must be defined in  every  translation  unit  in  which  it  is
  implicitly   instantiated  (_temp.inst_)  or  explicitly  instantiated
  (_temp.explicit_); no diagnostic is required.   An  exported  template
  need  only  be declared (and not necessarily defined) in a translation
  unit in which it is instantiated.  A template function  declared  both
  exported and inline is just inline and not exported.

8 [Note:  an implementation may require that a translation unit contain­
  ing the definition of an exported  template  be  compiled  before  any
  translation unit containing an instantiation of that template.  ]

  14.1  Template parameters                                 [temp.param]

1 The syntax for template-parameters is:
          template-parameter:
                  type-parameter
                  parameter-declaration
          type-parameter:
                  class identifieropt
                  class identifieropt = type-id
                  typename identifieropt
                  typename identifieropt = type-id
                  template < template-parameter-list > class  identifieropt
                  template < template-parameter-list > class  identifieropt = template-name
  There  is  no semantic difference between class and typename in a tem­
  plate-parameter.  typename followed by an unqualified-id names a  tem­
  plate  type  parameter.  typename followed by a qualified-name denotes
  the type in a non-type parameter-declaration.  A storage  class  shall
  not  be  specified in a template-parameter declaration.  [Note: a tem­
  plate parameter may be a class template.  For example,
          template<class T> class myarray { /* ... */ };

          template<class K, class V, template<class T> class C = myarray>
          class Map {
                  C<K> key;
                  C<V> value;
                  // ...
          };
   --end note]

2 A type-parameter defines its identifier to be a type-name (if declared
  with  class  or typename) or template-name (if declared with template)
  in the scope of the template declaration.  [Note: because of the  name
  look  up  rules,  a  template-parameter  that  could be interpreted as
  either a non-type template-parameter or a type-parameter (because  its

  identifier  is  the  name  of an already existing class) is taken as a
  type-parameter.  For example,
          class T { /* ... */ };
          int i;

          template<class T, T i> void f(T t)
          {
                  T t1 = i;      // template-parameters T and i
                  ::T t2 = ::i;  // global namespace members T and i
          }
  Here, the template f has a type-parameter called  T,  rather  than  an
  unnamed non-type template-parameter of class T.  ]

3 A non-type template-parameter shall have one of the following (option­
  ally cv-qualified) types:

  --integral type, accepting an integral constant expression as an argu­
    ment,

  --enumeration  type,  accepting  an integral constant expression as an
    argument,

  --pointer to object, accepting an address constant  expression  desig­
    nating a named object with external linkage,

  --reference  to  object,  accepting an lvalue expression designating a
    named object with external linkage,

  --pointer to function, accepting an  expression  of  type  pointer  to
    function designating a function with external linkage,

  --reference  to function, accepting an lvalue expression designating a
    function with external linkage,

  --pointer to member, accepting an address constant  expression  desig­
    nating a named member of a class.

4 [Note:  other  types are disallowed either explicitly below or implic­
  itly  by  the  rules  governing   the   form   of   template-arguments
  (_temp.arg_).  ] The top-level cv-qualifiers on the template-parameter
  are ignored when determining its type.

5 A non-type non-reference template-parameter  is  not  an  lvalue.   It
  shall  not  be assigned to or in any other way have its value changed.
  A non-type non-reference template-parameter cannot  have  its  address
  taken.  When a non-type non-reference template-parameter is used as an
  initializer for a reference, a temporary is always used.  [Example:

          template<const X& x, int i> void f()
          {
                  i++; // error: change of template-parameter value

                  &x; // ok
                  &i; // error: address of non-reference template-parameter

                  int& ri = i; // error: non-const reference bound to temporary
                  const int& cri = i; // ok: const reference bound to temporary
          }
   --end example]

6 A non-type template-parameter shall not be of type void.   A  non-type
  template-parameter shall not be of floating type.  [Example:
          template<double d> class X;    // error
          template<double* pd> class Y;  // ok
          template<double& rd> class Z;  // ok
   --end example]

7 The  notion  of  "array type decay" does not apply to template-parame­
  ters.  [Example:
          template<int a[5]> struct S { /* ... */ };
          int v[5];
          int* p = v;
          S<v> x; // fine
          S<p> y; // error
   --end example]

8 A default template-argument is a type, value,  or  template  specified
  after  =  in a template-parameter.  A default template-argument may be
  specified for both a type and non-type template-parameter.  A  default
  template-argument  may be specified in a class template declaration or
  a class template definition.  A default template-argument shall not be
  specified  in  a  function template declaration or a function template
  definition.  The set of default template-arguments available  for  use
  with  a  template in a translation unit shall be provided by the first
  declaration of the template in that translation unit.

9 If a template-parameter has a default  template-argument,  all  subse­
  quent  template-parameters shall have a default template-argument sup­
  plied.  [Example:
          template<class T1 = int, class T2> class B; // error
   --end example]

  14.2  Names of template specializations                   [temp.names]

1 A template specialization (_temp.spec_) can be referred to by  a  tem­
  plate-id:
          template-id:
                  template-name < template-argument-list >
          template-name:
                  identifier

          template-argument-list:
                  template-argument
                  template-argument-list , template-argument
          template-argument:
                  assignment-expression
                  type-id
                  template-name
  [Note:  the  name look up rules (_basic.lookup_) are used to associate
  the use of a name with a template declaration; that is, to identify  a
  name as a template-name.  ]

2 For  a  template-name to be explicitly qualified by the template argu­
  ments, the name must be known to refer to a template.

3 After name look up (_basic.lookup_) finds that a name is  a  template-
  name,  if  this  name is followed by a <, the < is always taken as the
  beginning of a template-argument-list and never as a name followed  by
  the  less-than  operator.   When parsing a template-id, the first non-
  nested >1) is taken as the end of  the  template-argument-list  rather
  than a greater-than operator.  [Example:
          template<int i> class X { /* ... */ };

          X< 1>2 >        x1; // syntax error
          X<(1>2)>        x2; // ok

          template<class T> class Y { /* ... */ };
          Y< X<1> >       x3; // ok
          Y<X<6>> 1> >    x4; // ok: Y< X< (6>>1) > >
   --end example]

4 When  the name of a member template specialization appears after .  or
  -> in a postfix-expression, or after :: in a qualified-id that explic­
  itly  depends on a template-argument (_temp.dep_), the member template
  name must be prefixed by the keyword template.  Otherwise the name  is
  assumed to name a non-template.  [Example:
          class X {
          public:
                  template<size_t> X* alloc();
          };
          void f(X* p)
          {
                  X* p1 = p->alloc<200>();
                          // ill-formed: < means less than

                  X* p2 = p->template alloc<200>();
                          // fine: < starts explicit qualification
          }
   --end example]

  _________________________
  1) A > that encloses the type-id of a dynamic_cast, static_cast, rein­
  terpret_cast  or  const-cast  is  considered nested for the purpose of
  this description.

5 If a name prefixed by the keyword template in this way is not the name
  of a member function template, the program is ill-formed.

6 A template-id that names a class template specialization is  a  class-
  name (_class_).

  14.3  Template arguments                                    [temp.arg]

1 The  types  of the template-arguments specified in a template-id shall
  match the types specified for the template in its  template-parameter-
  list.  [Example:
          template<class T> class Array {
                  T* v;
                  int sz;
          public:
                  explicit Array(int);
                  T& operator[](int);
                  T& elem(int i) { return v[i]; }
                  // ...
          };
          Array<int> v1(20);
          typedef complex<double> dcomplex; // complex is a standard
                                            // library template
          Array<dcomplex> v2(30);
          Array<dcomplex> v3(40);

          v1[3] = 7;
          v2[3] = v3.elem(4) = dcomplex(7,8);
    --end  example]  If  the use of a template-argument gives rise to an
  ill-formed construct in the implicit instantiation of a template  spe­
  cialization, the instantiation is ill-formed.

2 In  a template-argument, an ambiguity between a type-id and an expres­
  sion is resolved to a type-id.  [Example:
          template<class T> void f();
          template<int I> void f();

          void g()
          {
                  f<int()>(); // ``int()'' is a type-id: call the first f()
          }
   --end example]

3 A template-argument for a  non-type  non-reference  template-parameter
  shall be an integral constant-expression of integral type, the name of
  a non-type non-reference template parameter, the address of an  object
  or  a  function  with external linkage, or a non-overloaded pointer to
  member.  The address of an object or function shall  be  expressed  as
  &f,  plain  f (for function only), or &X::f where f is the function or
  object name.  In the case of &X::f, X shall be a (possibly  qualified)
  name  of a class and f the name of a static member of X.  A pointer to
  member shall be expressed as &X::m where X is a  (possibly  qualified)
  name  of  a  class  and m is the name of a non-static member of X.  In
  particular, a string  literal  (_lex.string_)  is  not  an  acceptable

  template-argument  because a string literal is an object with internal
  linkage.  [Example:
          template<class T, char* p> class X {
                  // ...
                  X(const char* q) { /* ... */ }
          };

          X<int,"Studebaker"> x1; // error: string literal as template-argument

          char p[] = "Vivisectionist";
          X<int,p> x2; // ok
   --end example]

4 Addresses of array elements and of non-static class members shall  not
  be used as template-arguments.  [Example:
          template<int* p> class X { };

          int a[10];
          struct S { int m; static int s; } s;

          X<&a[2]> x3; // error: address of array element
          X<&s.m> x4;  // error: address of non-static member
          X<&s.s> x5;  // error: &S::s must be used
          X<&S::s> x6; // ok: address of static member
   --end example]

5 A  non-type  template-parameter that is a reference shall not be bound
  to a temporary, an unnamed lvalue, or a named  lvalue  that  does  not
  have external linkage.  [Example:
          template<const int& CRI> struct B { /* ... */ };

          B<1> b2; // error: temporary required for template argument

          int c = 1;
          B<c> b1; // ok
   --end example]

6 Standard  conversions  (_conv_) are applied to an expression used as a
  template-argument for a non-type template-parameter to bring it to the
  type of its corresponding template-parameter.  [Example:
          template<const int* pci> struct X { /* ... */ };
          int ai[10];
          X<ai> xi;  // array to pointer and qualification conversions

          struct Base { /* ... */ };
          struct Derived : Base { /* ... */ };
          template<Base& b> struct Y { /* ... */ };
          Derived d;
          Y<d> yd;   // derived to base conversion
   --end example]

7 An  argument  to  a non-type template-parameter of pointer to function
  type shall have exactly the type specified by the  template-parameter.
  [Note:  this  allows  selection from a set of overloaded functions.  ]

  [Example:
          void f(char);
          void f(int);

          template<void (*pf)(int)> struct A { /* ... */ };

          A<&f> a; // selects f(int)
   --end example]

8 If a declaration acquires a function type through a  template-argument
  of  function  type and this causes a declaration that does not use the
  syntactic form of a function declarator to  have  function  type,  the
  program is ill-formed.  [Example:
          template<class T> struct A {
                  static T t;
          };
          typedef int function();
          A<function> a;  // ill-formed: would declare A<function>::t
                          // as a static member function
   --end example]

9 A  local  type, a type with no linkage or an unnamed type shall not be
  used as a template-argument for a template type-parameter.  [Example:
          void f()
          {
                  struct S { /* ... */ };

                  X<S> x3; // error: local type used as template-argument
          }
   --end example]

10For a template-argument of class type, the template definition has  no
  special  access  rights  to  the  inaccessible members of the template
  argument type.  The name of a template-argument shall be accessible at
  the point where it is used as a template-argument.  [Example:
          template<class T> class X { /* ... */ };

          class Y {
          private:
                  struct S { /* ... */ };
                  X<S> x;  // ok: S is accessible
          };

          X<Y::S> y; // error: S not accessible
   --end example]

11When default template-arguments are used, a template-argument list can
  be empty.  In that case the empty <> brackets shall still be  used  as
  the template-argument-list.  [Example:
          template<class T = char> class String;
          String<>* p; // ok: String<char>
          String* q;   // syntax error
   --end example]

12An  explicit  destructor  call (_class.dtor_) for an object that has a
  type that is a class template specialization  may  explicitly  specify
  the template-arguments.  [Example:
          template<class T> struct A {
                  ~A();
          };
          void main() {
                  A<int>* p;
                  p->A<int>::~A(); // ok: destructor call
                  p->A<int>::~A<int>(); // ok: destructor call
          }
   --end example]

  14.4  Type equivalence                                     [temp.type]

1 Two template-ids refer to the same class or function if their template
  names are identical, they refer to the same template, their type  tem­
  plate-arguments  are  the same type and, their non-type template-argu­
  ments have identical values.  [Example:
          template<class E, int size> class buffer { /* ... */ };
          buffer<char,2*512> x;
          buffer<char,1024> y;
  declares x and y to be of the same type, and
          template<class T, void(*err_fct)()> class list { /* ... */ };
          list<int,&error_handler1> x1;
          list<int,&error_handler2> x2;
          list<int,&error_handler2> x3;
          list<char,&error_handler2> x4;
  declares x2 and x3 to be of the same type.  Their  type  differs  from
  the types of x1 and x4.  ]

  14.5  Template declarations                               [temp.decls]

1 A template-id, that is, the template-name followed by a template-argu­
  ment-list shall not be specified in the declaration of a primary  tem­
  plate declaration.  [Example:
          template<class T1, class T2, int I> class A<T1, T2, I> { }; // error
          template<class T1, int I> void sort<T1, I>(T1 data[I]);     // error
    --end  example] [Note: however, this syntax is allowed in class tem­
  plate partial specializations (_temp.class.spec_).  ]

  14.5.1  Class templates                                   [temp.class]

1 A class template defines the layout and operations  for  an  unbounded
  set  of  related  types.  [Example: a single class template List might
  provide a common definition for list of int, list of float,  and  list
  of pointers to Shapes.  ]

2 [Example: An array class template might be declared like this:

          template<class T> class Array {
              T* v;
              int sz;
          public:
              explicit Array(int);
              T& operator[](int);
              T& elem(int i) { return v[i]; }
              // ...
          };
  The  prefix  template  <class  T>  specifies  that a template is being
  declared and that a type-name T will be used in the  declaration.   In
  other words, Array is a parameterized type with T as its parameter.  ]

3 When a member function, a member class, a static data member or a mem­
  ber  template of a class template is defined outside of the class tem­
  plate definition, the names of template parameters used in the defini­
  tion  of the member may be different from the template parameter names
  used in the class template definition.   The  template  argument  list
  following  the class template name in the member definition shall name
  the parameters in the same order as the one used in  the  member  tem­
  plate parameter list.  [Example:
          template<class T1, class T2> struct A {
              void f1();
              void f2();
          };

          template<class T2, class T1> void A<T2,T1>::f1() { } //ok
          template<class T2, class T1> void A<T1,T2>::f2() { } //error
   --end example]

  +-------                      BEGIN BOX 1                     -------+
  Gibbons feels that the above sentence and example are no longer appli­
  cable after resolution 6.31 from N0890 = 96-0059, that is the  follow­
  ing should now be legal:
          template<class T2, class T1> void A::f1() { } //ok
  Corfield  is not convinced that was the intent of Core III and that we
  should make an explicit decision on this (it seems the right thing  to
  do).
  +-------                       END BOX 1                      -------+

  14.5.1.1  Member functions of class templates          [temp.mem.func]

1 A  member function of a class template is implicitly a member function
  template with the template-parameters of its  class  template  as  its
  template-parameters.

2 A  member  function  template may be defined outside of the class tem­
  plate definition in which it is declared.  [Example:

          template<class T> class Array {
              T* v;
              int sz;
          public:
              explicit Array(int);
              T& operator[](int);
              T& elem(int i) { return v[i]; }
              // ...
          };
  declares three function templates.  The subscript  function  might  be
  defined like this:
          template<class T> T& Array<T>::operator[](int i)
          {
              if (i<0 || sz<=i) error("Array: range error");
              return v[i];
          }
   --end example]

3 The  template-arguments  for a class member function are determined by
  the template-arguments of the type of the object for which the  member
  function    is    called.    [Example:   the   template-argument   for
  Array<T>::operator[]() will be determined by the Array  to  which  the
  subscripting operation is applied.
          Array<int> v1(20);
          Array<dcomplex> v2(30);

          v1[3] = 7;              // Array<int>::operator[]()
          v2[3] = dcomplex(7,8);  // Array<dcomplex>::operator[]()
   --end example]

  14.5.1.2  Member classes of class templates           [temp.mem.class]

1 A member class of a class template is implicitly a class template with
  the template-parameters of its class template as its  template-parame­
  ters.

2 A member class template may be defined outside the class template def­
  inition in which it is declared.  [Note:  the  member  class  template
  must  be  defined before the first use of the member which requires an
  instantiation (_temp.inst_).  For example,
          template<class T> struct A {
                  class B;
          };
          A<int>::B* b1;  // ok: requires A to be defined but not A::B
          template<class T> class A<T>::B { };
          A<int>::B  b2;  // ok: requires A::B to be defined
   --end note]

  14.5.1.3  Static data members of class templates         [temp.static]

1 A static data member of a class template is implicitly a  static  data
  member  template with the template-parameters of its class template as
  its template-parameters.  A template definition for such a static data
  member  may  be provided in a namespace scope enclosing the definition

  of the static member's class template.  [Example:
          template<class T> class X {
                  static T s;
          };
          template<class T> T X<T>::s = 0;
   --end example]

  14.5.2  Member templates                                    [temp.mem]

1 A template can be declared within a class or class  template;  such  a
  template  is  called  a  member  template.   A  member template can be
  defined within or outside its class definition or class template defi­
  nition.  A member template of a class template that is defined outside
  of its class template definition shall be specified with the template-
  parameters  of  the class template followed by the template-parameters
  of the member template.  [Example:
          template<class T> class string {
          public:
                  template<class T2> int compare(const T2&);
                  template<class T2> string(const string<T2>& s) { /* ... */ }
                  // ...
          };

          template<class T> template<class T2> int string<T>::compare(const T2& s)
          {
                  // ...
          }
   --end example]

2 Access control rules apply to member template names  (_class.access_).

3 A  local  class shall not have member templates.  Access control rules
  apply to member template names.  A destructor shall not  be  a  member
  template.   A  normal (non-template) member function with a given name
  and type and a member function template of the same name that could be
  used  to  generate  a  specialization  of the same type can be both be
  declared in a class.  When both exist, a reference refers to the  non-
  template  unless  an  explicit  template  argument  list  is supplied.
  [Example:
          template <class T> struct A {
                  void f(int);
                  template <class T2> void f(T2);
          };

          template <> void A<int>::f(int) { }  // non-template member
          template <> template <> void A<int>::f<>(int) { }  // template member
          int main()
          {
                  A<char> ac;
                  ac.f(1);    // non-template
                  ac.f('c');  // template
                  ac.f<>(1);  // template
          }
   --end example]

4 A member function template shall not be virtual.  A specialization  of
  a member function template does not override a virtual function from a
  base class.  [Example:
          class B {
                  virtual void f(int);
          };
          class D : public B {
                  template <class T> void f(T);  // does not override B::f(int)
                  void f(int i) { f<>(i); }  // overriding function that calls
                                             // the template instantiation
          };
   --end example]

5 A specialization of a template conversion operator  is  referenced  in
  the  same  way  as a non-template conversion operator that converts to
  the same type.  [Example:
          struct A {
                  template <class T> operator T*();
          };
          template <class T> A::operator T*(){ return 0; }
          template <> A::operator char*(){ return 0; }  // specialization
          template A::operator void*();                 // explicit instantiation
          int main()
          {
                  A      a;
                  int*   ip;

                  ip = a.operator int*();  // explicit call to template operator
                                           // A::operator int*()
          }
  ]

6 If more than one conversion template can produce  the  required  type,
  the  partial ordering rules (_temp.func.order_) are used to select the
  "most specialized" version  of  the  template  that  can  produce  the
  required  type.   As  with other conversion functions, the type of the
  implicit this parameter is not considered.   [Note:  members  of  base
  classes  are  considered  equally  with  members of the derived class,
  except that a derived class conversion function  hides  a  base  class
  conversion function that converts to the same type.   --end note]

  14.5.3  Friends                                          [temp.friend]

1 A friend function of a class template can be a function template or an
  ordinary (non-template) function.  [Example:
          template<class T> class task {
              // ...
              friend void next_time();
              friend task<T>* preempt(task<T>*);
              friend task* prmt(task*);           // task is task<T>
              friend class task<int>;
              // ...
          };
  Here, next_time() and task<int> become friends of  all  task  classes,

  and  each  task has appropriately typed functions preempt() and prmt()
  as friends.  The preempt functions might be defined as a  template  as
  follows
          template<class T> task<T>* preempt(task<T>* t) { /* ... */ }
   --end example]

2 A  friend  template  may  be  declared within a non-template class.  A
  friend function template may be defined within a  non-template  class.
  In  these cases, all specializations of the class or function template
  are friends of the class granting friendship.  [Example:
          class A {
                  template<class T> friend class B; // ok
                  template<class T> friend void f(T){ /* ... */ } // ok
          };
   --end example]

3 When a function is defined in a friend function declaration in a class
  template,  the  function  is  defined when the class template is first
  instantiated.  The function is defined  even  if  it  is  never  used.
  [Note:  if  the function definition is ill-formed for a given special­
  ization of the enclosing class template,  the  program  is  ill-formed
  even if the function is never used.   --end note]

4 A  member of a class template may be declared to be a friend of a non-
  template class.  In this case, the corresponding  member  function  of
  every  specialization  of  the class template is a friend of the class
  granting friendship.  [Example:
          template<class T> struct A {
                  struct B { };
                  void f();
          };

          class C {
                  template<class T> friend struct A<T>::B;
                  template<class T> friend void A<T>::f();
          };
   --end example]

5 [Note: a friend declaration may first declare a member of an enclosing
  namespace scope (_temp.inject_).  ]

6 A friend template shall not be declared in a local class.

  14.5.4  Class template partial specializations       [temp.class.spec]

1 A  primary  class  template declaration is one in which the class tem­
  plate name is an identifier.  A  template  declaration  in  which  the
  class  template  name is a template-id, is a partial specialization of
  the class template named in the template-id.  A partial specialization
  of a class template provides an alternative definition of the template
  that is used instead of the primary definition when the arguments in a
  specialization   match  those  given  in  the  partial  specialization
  (_temp.class.spec.match_).  The primary  template  shall  be  declared
  before  any  specializations  of  that  template.   If  a  template is

  partially  specialized  then  that  partial  specialization  shall  be
  declared before the first use  of  that  partial  specialization  that
  would cause an implicit instantiation to take place, in every transla­
  tion unit in which such a use occurs.   Each  class  template  partial
  specialization  is  a  distinct template and definitions shall be pro­
  vided  for  the  members  of   a   template   partial   specialization
  (_temp.class.spec.mfunc_).

2 [Example:
          template<class T1, class T2, int I> class A             { }; // #1
          template<class T, int I>            class A<T, T*, I>   { }; // #2
          template<class T1, class T2, int I> class A<T1*, T2, I> { }; // #3
          template<class T>                   class A<int, T*, 5> { }; // #4
          template<class T1, class T2, int I> class A<T1, T2*, I> { }; // #5
  The  first declaration declares the primary (unspecialized) class tem­
  plate.  The second and subsequent declarations  declare  partial  spe­
  cializations of the primary template.  ]

3 The  template  parameters  are specified in the angle bracket enclosed
  list that immediately follows the keyword template.  For partial  spe­
  cializations, the template argument list is explicitly written immedi­
  ately following the class template name.  For primary templates,  this
  list is implicitly described by the template parameter list.  Specifi­
  cally, the order of the template arguments is the  sequence  in  which
  they  appear  in  the template parameter list.  [Example: the template
  argument list for the primary template in the example  above  is  <T1,
  T2, I>.  ] [Note: the template argument list shall not be specified in
  the primary template declaration. For example,
          template<class T1, class T2, int I> class A<T1, T2, I>  { }; // error
   --end note]

4 A non-type argument is non-specialized if it is the name of a non-type
  parameter.  All other non-type arguments are specialized.

5 Within  the  argument list of a class template partial specialization,
  the following restrictions apply:

  --A partially  specialized  non-type  argument  expression  shall  not
    involve a template parameter of the specialization.  [Example:
              template <int I, int J> struct B {};
              template <int I> struct B<I, I*2> {};  // error
     --end example]

  --The type of a specialized argument shall not be dependent on another
    parameter of the specialization.  [Example:
              template <class T, T t> struct C {};
              template <class T> struct C<T, 1>;  // error
     --end example]

  --The argument list of the specialization shall not  be  identical  to
    the implicit argument list of the primary template.

6
  +-------                      BEGIN BOX 2                     -------+

  Change:

7 Corfield: Previously Box 18 referred to the second bullet above noting
  that it did not disallow certain partial specialisations  that  should
  clearly be ill-formed. In the light of the clarification of "dependent
  name" I have amended the bullet  to  disallow  those  forms  based  on
  dependency of arguments on each other.
  +-------                       END BOX 2                      -------+

  The  template  parameter  list  of  a specialization shall not contain
  default template argument values.2)

  14.5.4.1  Matching of class template           [temp.class.spec.match]
       partial specializations

1 When a class template is used in a context that requires an instantia­
  tion of the class, it is necessary to determine whether the instantia­
  tion  is to be generated using the primary template or one of the par­
  tial specializations.  This is done by matching the template arguments
  of  the class template specialization with the template argument lists
  of the partial specializations.

  --If exactly one matching specialization is found,  the  instantiation
    is generated from that specialization.

  --If more than one matching specialization is found, the partial order
    rules (_temp.class.order_) are used to determine whether one of  the
    specializations is more specialized than the others.  If none of the
    specializations is more specialized than all of the  other  matching
    specializations, then the use of the class template is ambiguous and
    the program is ill-formed.

  --If no matches are found, the instantiation  is  generated  from  the
    primary template.

2 A partial specialization matches a given actual template argument list
  if the template arguments of the partial specialization can be deduced
  from the actual template argument list (_temp.deduct_).  [Example:
          A<int, int, 1>   a1;  // uses #1
          A<int, int*, 1>  a2;  // uses #2, T is int, I is 1
          A<int, char*, 5> a3;  // uses #4, T is char
          A<int, char*, 1> a4;  // uses #5, T1 is int, T2 is char, I is 1
          A<int*, int*, 2> a5;  // ambiguous: matches #3 and #5
   --end example]

3 A  non-type template argument can also be deduced from the value of an
  actual template argument of a non-type parameter of the  primary  tem­
  plate.  [Example: the declaration of a2 above.  ]

4 In  a type name that refers to a class template specialization, (e.g.,
  A<int, int, 1>) the argument list must match  the  template  parameter
  _________________________
  2) There is no way in which they could be used.

  list of the primary template.  The template arguments of a specializa­
  tion are deduced from the arguments of the primary template.

  14.5.4.2  Partial ordering of class template        [temp.class.order]
       specializations

1 For  two class template partial specializations, the first is at least
  as specialized as the second if:

  --the type arguments of the first  template's  argument  list  are  at
    least as specialized as those of the second template's argument list
    using the ordering rules for function templates (_temp.func.order_),
    and

  --each  non-type  argument of the first template's argument list is at
    least as specialized as that of the second template's argument list.

2 A  non-type  argument  is  at least as specialized as another non-type
  argument if:

  --both are formal arguments, or

  --the first is a value and the second is a formal argument, or

  --both are the same value.

3 A class template  partial  specialization  is  more  specialized  than
  another  if,  and  only if, it is at least as specialized as the other
  class template partial specialization and that class template  partial
  specialization is not at least as specialized as the first.  Otherwise
  the two class template partial specializations are unordered.   [Note:
  these  rules  do  not  cover all sets of partial specializations. Some
  sets are therefore considered unordered even when an ``obvious'' order
  might seem to exist. For example:
          template<int I, int J, class T> class X {};            // #1
          template<int I, int J>          class X<I, J, int> {}; // #2
          template<int I>                 class X<I, I, int> {}; // #3
  This  set is unordered even though #3 might look more specialized than
  #2.   --end note]

  14.5.4.3  Members of class template            [temp.class.spec.mfunc]
       specializations

1 The  template  parameter  list of a member of a class template partial
  specialization shall match the template parameter list  of  the  class
  template partial specialization.  The template argument list of a mem­
  ber of a class template partial specialization shall  match  the  tem­
  plate  argument  list of the class template partial specialization.  A
  class template specialization is a distinct template.  The members  of
  the class template partial specialization are unrelated to the members
  of the primary template.  Class template partial  specialization  mem­
  bers  that  are  used  in  a  way  that requires a definition shall be
  defined; the definitions of members of the primary template are  never
  used   as   definitions  for  members  of  a  class  template  partial

  specialization.  An explicit specialization of a  member  of  a  class
  template  partial  specialization  is  declared  in the same way as an
  explicit specialization of the primary template.  [Example:
          // primary template
          template<class T, int I> struct A {
                  void f();
          };

          template<class T, int I> void A<T,I>::f() { }
          // class template partial specialization
          template<class T> struct A<T,2> {
                  void f();
                  void g();
                  void h();
          };

          // member of class template partial specialization
          template<class T> void A<T,2>::g() { }
          // explicit specialization
          template<> void A<char,2>::h() { }

          int main()
          {
                  A<char,0> a0;
                  A<char,2> a2;
                  a0.f(); // ok, uses definition of primary template's member
                  a2.g(); // ok, uses definition of
                          // partial specialization's member
                  a2.h(); // ok, uses definition of
                          // explicit specialization's member
                  a2.f(); // ill-formed, no definition of f for A<T,2>
                          // the primary template is not used here
          }
   --end example]

  14.5.5  Function templates                                  [temp.fct]

1 A function template defines an unbounded  set  of  related  functions.
  [Example: a family of sort functions might be declared like this:
          template<class T> class Array { };
          template<class T> void sort(Array<T>&);
   --end example]

2 A  function  template  can be overloaded with other function templates
  and with normal (non-template) functions.  A normal  function  is  not
  related  to  a function template (i.e., it is never considered to be a
  specialization), even if it has the same name and  type  as  a  poten­
  tially generated function template specialization.3)
  _________________________
  3) That is, declarations of non-template functions do not merely guide
  overload resolution of template functions with the same name.  If such
  a  non-template  function is used in a program, it must be defined; it
  will not be implicitly instantiated using the function template  defi­
  nition.

  14.5.5.1  Function template overloading               [temp.over.link]

1 It  is  possible  to overload function templates so that two different
  function template specializations have the same type.  [Example:
          // file1.c                     // file2.c
          template<class T>              template<class T>
              void f(T*);                    void f(T);
          void g(int* p) {               void h(int* p) {
              f(p); // call                  f(p); // call
                    // f<int>(int*)                // f<int*>(int*)
          }                              }
   --end example]

2 Such specializations are distinct functions and do not violate the one
  definition rule (_basic.def.odr_).

3 The  signature  of  a function template specialization consists of the
  signature of the function template and of the  actual  template  argu­
  ments (whether explicitly specified or deduced).

4 The  signature  of a function template consists of its function signa­
  ture, its return type and its template parameter list.  The  names  of
  the  template  parameters  are  significant  only for establishing the
  relationship between the template parameters and the rest of the  sig­
  nature.

  14.5.5.2  Partial ordering of function               [temp.func.order]
       templates

1 Given two function templates, whether one  is  more  specialized  than
  another  can  be  determined by transforming each template in turn and
  using argument deduction (_temp.deduct_) to compare it to the other.

2 The transformation used is:

  --For each type template parameter, synthesize a unique type and  sub­
    stitute  that  for each occurrence of that parameter in the function
    parameter list.

  --For each non-type template parameter, synthesize a unique  value  of
    the appropriate type and substitute that for each occurrence of that
    parameter in the function parameter list.

3 Using the transformed function parameter list, perform argument deduc­
  tion against the other function template.  The transformed template is
  at least as specialized as the other if, and only  if,  the  deduction
  succeeds  and  the  deduced parameter types are an exact match (so the
  deduction does not rely on implicit conversions).

4 A template is more specialized than another if, and only if, it is  at
  least as specialized as the other template and that template is not at
  least as specialized as the first.  [Example:

          template<class T> struct A { A(); };

          template<class T> void f(T);
          template<class T> void f(T*);
          template<class T> void f(const T*);

          template<class T> void g(T);
          template<class T> void g(T&);

          template<class T> void h(const T&);
          template<class T> void h(A<T>&);
          void m() {
                  const int *p;
                  f(p);  // f(const T*) is more specialized than f(T) or f(T*)
                  float x;
                  g(x);  // Ambiguous: g(T) or g(T&)
                  A<int> z;
                  h(z);  // Ambiguous: h(A<T>&) and h(const T&) are not comparable
                  const A<int> z2;
                  h(z2); // h(const T&) is called because h(A<T>&) is not callable
          }
   --end example]

  14.6  Name resolution                                       [temp.res]

1 A name used in a template is assumed not to name  a  type  unless  the
  applicable  name  lookup finds a type name or the name is qualified by
  the keyword typename.  [Example:
          // no B declared here

          class X;

          template<class T> class Y {
                  class Z; // forward declaration of member class

                  void f() {
                          X* a1;    // declare pointer to X
                          T* a2;    // declare pointer to T
                          Y* a3;    // declare pointer to Y<T>
                          Z* a4;    // declare pointer to Z
                          typedef typename T::A TA;
                          TA* a5;   // declare pointer to T's A
                          typename T::A* a6;   // declare pointer to T's A
                          T::A* a7; // T::A is not a type name:
                          // multiply T::A by a7
                          B* a8;    // B is not a type name:
                          // multiply B by a8
                  }
          };
   --end example]

2 A qualified-name that refers to a type and that depends on a template-
  parameter  (_temp.dep_)  shall  be prefixed by the keyword typename to
  indicate that the qualified-name denotes a type.

          elaborated-type-specifier:
                  . . .
                  typename ::opt nested-name-specifier identifier full-template-argument-listopt
                  . . .

          full-template-argument-list:
                  < template-argument-list >

3 If a specialization of a template is instantiated for a  set  of  tem­
  plate-arguments such that the qualified-name prefixed by typename does
  not denote a type, the specialization is ill-formed.  The usual quali­
  fied  name lookup (_basic.lookup.qual_) is used to find the qualified-
  name even in the presence of typename.  [Example:
          struct A {
                  struct X { };
                  int X;
          };
          template<class T> void f(T t) {
                  typename T::X x; // ill-formed: finds the data member X
                                   // not the member type X
          }
   --end example]

4 Knowing which names are type names allows the syntax of every template
  definition  to  be  checked.  No diagnostic shall be issued for a tem­
  plate definition for which a valid specialization  can  be  generated.
  If no valid specialization can be generated for a template definition,
  and that template is not instantiated, it is  unspecified  whether  or
  not  an implementation is required to issue a diagnostic.  [Note: if a
  template is instantiated, errors will be diagnosed  according  to  the
  other rules in this Standard.  Exactly when these errors are diagnosed
  is a quality of implementation issue.  ] [Example:
          int j;
          template<class T> class X {
                  // ...
                  void f(T t, int i, char* p)
                  {
                          t = i;  // diagnosed if X::f is instantiated
                                  // and the assignment to t is an error
                          p = i;  // may be diagnosed even if X::f is
                                  // not instantiated
                          p = j;  // may be diagnosed even if X::f is
                                  // not instantiated
                  }
                  void g(T t) {
                          +;      // may be diagnosed even if X::g is
                                  // not instantiated
                  }
          };
   --end example]

5 Three kinds of names can be used within a template definition:

  --The name  of  the  template  itself,  the  names  of  the  template-

    parameters  (_temp.param_),  and  names declared within the template
    itself.

  --Names dependent on a template-argument (_temp.dep_).

  --Names from scopes which are visible within the template  definition.

6 When looking for the declaration of a name used in a template function
  definition or static data member template definition, the usual lookup
  rules (_basic.lookup.unqual_, _basic.lookup.koenig_) are used for non­
  dependent names.  The lookup of names dependent on the template  argu­
  ments  is  postponed  until  the  actual  template  argument  is known
  (_temp.dep_).  [Example:
          #include <iostream>
          using namespace std;

          template<class T> class Set {
                  T* p;
                  int cnt;
          public:
                  Set();
                  Set<T>(const Set<T>&);
                  void printall()
                  {
                          for (int i = 0; i<cnt; i++)
                                  cout << p[i] << '\n';
                  }
                  // ...
          };
  in the example, i is the local variable i declared in printall, cnt is
  the member cnt declared in Set, and cout is the standard output stream
  declared in iostream.  However, not every  declaration  can  be  found
  this  way;  the  resolution  of some names must be postponed until the
  actual template-arguments are known.  For  example,  even  though  the
  name  operator<<  is  known  within the definition of printall() and a
  declaration of it can be found in <iostream>, the  actual  declaration
  of  operator<<  needed to print p[i] cannot be known until it is known
  what type T is (_temp.dep_).  ]

7 If a name does not  depend  on  a  template-argument  (as  defined  in
  _temp.dep_),  a  declaration  (or  set  of declarations) for that name
  shall be in scope at the point where the name appears in the  template
  definition;  the  name  is  bound to the declaration (or declarations)
  found at that point and this binding is not affected  by  declarations
  that are visible at the point of instantiation.

  +-------                      BEGIN BOX 3                     -------+
  Change:

8 The previous wording did not require that a declaration be in scope at
  the point of the template definition for names not dependent on a tem­
  plate argument.
  +-------                       END BOX 3                      -------+

  [Example:
          void f(char);

          template<class T> void g(T t)
          {
                  f(1);     // f(char)
                  f(T(1));  // dependent
                  f(t);     // dependent
                  dd++;      // not dependent
                             // error: declaration for dd not found
          }
          void f(int);

          double dd;
          void h()
          {
                  g(2);   // will cause one call of f(char) followed
                          //  by two calls of f(int)
                  g('a'); // will cause three calls of f(char)
          }
   --end example]

  14.6.1  Locally declared names                            [temp.local]

1 Within  the  scope of a class template, the name of the template, when
  not followed by <, is equivalent to the name of the template  followed
  by the template-parameters enclosed in <>.

  +-------                      BEGIN BOX 4                     -------+
  Change:

2 The previous sentence only applied to the unqualified name of the tem­
  plate.  Now, even if the name of the template  is  qualified,  if  the
  template  parameters  are omitted, this name is equivalent to the name
  of the template followed by the template-parameters enclosed in <>.
  +-------                       END BOX 4                      -------+

  [Example: the constructor for Set can  be  referred  to  as  Set()  or
  Set<T>().  ] Other specializations (_temp.expl.spec_) of the class can
  be referred to by explicitly qualifying the  template  name  with  the
  appropriate template-arguments.  [Example:
          template<class T> class X {
                  X* p;           // meaning X<T>
                  X<T>* p2;
                  X<int>* p3;
          };
   --end example]

3 Within  the  scope of a class template specialization, the name of the
  specialization is equivalent to the name of  the  specialization  fol­
  lowed by the template-arguments enclosed in <>.  [Example:

          template<class T> class Y;

          template<> class Y<int> {
                  Y* p;           // meaning Y<int>
          };
   --end example]

4 The  scope  of a template-parameter extends from its point of declara­
  tion until the end of its template.  A  template-parameter  hides  any
  entity with the same name in the enclosing scope.  [Note: this implies
  that a template-parameter can be used in the declaration of subsequent
  template-parameters  and their default arguments but cannot be used in
  preceding template-parameters or their default arguments.   For  exam­
  ple,
          template<class T, T* p, class U = T> class X { /* ... */ };
          template<class T> void f(T* p = new T);
  This  also implies that a template-parameter can be used in the speci­
  fication of base classes.  For example,
          template<class T> class X : public Array<T> { /* ... */ };
          template<class T> class Y : public T { /* ... */ };
  The use of a template-parameter as a base class implies that  a  class
  used as a template-argument must be defined and not just declared when
  the class template is instantiated.  ]

5 A template-parameter shall not be redeclared within its scope (includ­
  ing nested scopes).  A template-parameter shall not have the same name
  as the template name.  [Example:
          template<class T, int i> class Y {
                  int T;  // error: template-parameter redeclared
                  void f() {
                          char T; // error: template-parameter redeclared
                  }
          };

          template<class X> class X; // error: template-parameter redeclared
   --end example]

6 In the definition of a member of a class template that appears outside
  of  the  class  template definition, the name of a member of this tem­
  plate hides the name of a template-parameter.  [Example:
          template<class T> struct A {
                  struct B { /* ... */ };
                  void f();
          };

          template<class B> void A<B>::f()
          {
                  B b;  // A's B, not the template parameter
          }
   --end example]

  +-------                      BEGIN BOX 5                     -------+
  Gibbons suggests that we make this ill-formed instead of allowing  the
  hiding, in line with the status of redeclaring a function parameter in

  the outermost block of a function. Similarly, for the hiding with base
  class members below.
  +-------                       END BOX 5                      -------+

7 In the definition of a class template or in the definition of a member
  of such a template that appears outside of  the  template  definition,
  the  name  of a base class and, if the base class does not depend on a
  template-argument, the name of a base class member hides the name of a
  template-parameter with the same name.  [Example:
          struct A {
                  struct B { /* ... */ };
                  int a;
                  int Y;
          };

          template<class B, class a> struct X : A {
                  B b;  // A's B
                  a b;  // error: A's a isn't a type name
          };
   --end example]

  14.6.2  Dependent names                                     [temp.dep]

1 Inside  a  template,  some  constructs have semantics which may differ
  from one instantiation to another.  Such a construct  depends  on  the
  template argument.  In particular, types and expressions may depend on
  the type and or value of templates arguments and this  determines  the
  context  for  name lookup for certain names.  Expressions may be type-
  dependent (on the type of a template argument) or value-dependent  (on
  the  value  of a non-type template argument).  In an expression of the
  form:
        postfix-expression ( expression-listopt )
  where the postfix-expression is an identifier, the identifer denotes a
  dependent  name  if  and only if any of the expressions in the expres­
  sion-list is a type-dependent  expression  (_temp.dep.expr_).   If  an
  operand  of  an  operator is a type-dependent expression, the operator
  also denotes a dependent name.  Such names are unbound and are  looked
  up  at  the point of the template instantiation (_temp.point_) in both
  the context of the template definition and the context of the point of
  instantiation.

2 [Example:
          template<class T> struct X : B<T> {
                  typename T::A* pa;
                  void f(B<T>* pb) {
                          static int i = B<T>::i;
                          pb->j++;
                  }
          };
  the  base  class  name B<T>, the type name T::A, the names B<T>::i and
  pb->j explicitly depend on the template-argument.  This shows a  typi­
  cal dependent operator call:

          class Horse { /* ... */ };

          ostream& operator<<(ostream&,const Horse&);

          void hh(Set<Horse>& h)
          {
                  h.printall();
          }
  In the call of Set<Horse>::printall(), the meaning of the <<  operator
  used   to   print   p[i]   in  the  definition  of  Set<T>::printall()
  (_temp.res_), is
          operator<<(ostream&,const Horse&);
  This function takes an argument of type Horse and  is  called  from  a
  template  with  a template-parameter T for which the template-argument
  is Horse.  Because this function depends on a  template-argument,  the
  call  is  well-formed.   Some calls that depend on a template-argument
  type T are:

  1)The function called has a parameter that depends on T  according  to
    the  type  deduction  rules  (_temp.deduct_).   For  example,  f(T),
    f(Array<T>), and f(const T*).

  2)The type of the actual argument depends on T.  For example, f(T(1)),
    f(t), f(g(t)), and f(&t) assuming that t has the type T.

  3)A call is resolved by the use of a conversion to T without either an
    argument or a parameter of the called function being of a type  that
    depends on T as specified in (1) and (2).  For example,
              struct B { };
              struct T : B { };
              struct X { operator T(); };

              void f(B);

              void g(X x)
              {
                      f(x);  // meaning f( B( x.operator T() ) )
                             // so the call f(x) depends on T
              }
    This ill-formed template instantiation uses a function that does not
    depend on a template-argument:
              template<class T> class Z {
              public:
                      void f() const
                      {
                              g(1); // g() not found in Z's context.
                                    // ill-formed, even if g is declared at
                                    // the point of instantiation.  This
                                    // could be diagnosed either here or
                                    // at the point of instantiation.
                      }
              };

              void g(int);
              void h(const Z<Horse>& x)
              {
                      x.f(); // error: g(int) called by g(1) does not depend
                             // on template-argument ``Horse''
              }
    The call x.f() gives rise to the specialization:
              void Z<Horse>::f() { g(1); }
    The call g(1) would call g(int), but since that call does not depend
    on the template-argument Horse and because g(int) wasn't in scope at
    the point of the definition of the template, the call x.f() is  ill-
    formed.

3 On the other hand:
          void h(const Z<int>& y)
          {
                  y.f(); // fine: g(int) called by g(1) depends
                         // on template-argument ``int''
          }
  Here, the call y.f() gives rise to the specialization:
          void Z<int>::f() { g(1); }
  The  call  g(1)  calls g(int), and since that call depends on the tem­
  plate-argument int, the call y.f() is acceptable  even  though  g(int)
  wasn't in scope at the point of the template definition.  ]

4 In the definition of a class template or in the definition of a member
  of such template that appears outside of the template definition, if a
  base  class  of this template depends on a template-argument, the base
  class scope is not examined during name look up until the  class  tem­
  plate is instantiated.

  +-------                      BEGIN BOX 6                     -------+
  Unruh:  it  appears that names from dependent base classes can only be
  referenced with qualified names (otherwise they  are  considered  non-
  dependent  names) - we should state this explicitly. Corfield: is this
  true? I recall the discussions where this was clearly  the  intent  of
  Core III but it makes some code very unwieldy.
  +-------                       END BOX 6                      -------+

  [Example:
          typedef double A;
          template<class T> B {
                  typedef int A;
          };
          template<class T> struct X : B<T> {
                  A a;
          };
  X<T>::a  has  type  double.  The type name A binds to the typedef name
  defined in the global namespace scope, not to the typedef name defined
  in the base class B<T>.  ]

5 If  a  template-argument  is  a used as a base class, a member of that
  class cannot hide a name declared within a template, or  a  name  from
  the template's enclosing scopes.  [Example:

          struct A {
                  struct B { /* ... */ };
                  int a;
                  int Y;
          };

          int a;
          template<class T> struct Y : T {
                  struct B { /* ... */ };
                  B b;                     // The B defined in Y
                  void f(int i) { a = i; } // ::a
                  Y* p;                    // Y<T>
          };

          Y<A> ya;
  The  members  A::B,  A::a,  and A::Y of the template argument A do not
  affect the binding of names in Y<A>.  ]

  14.6.2.1  Dependent types                              [temp.dep.type]

1 A type is dependent if it is

  --a template parameter,

  --a qualified-id whose  nested-name-specifier  contains  a  class-name
    that  names  a dependent type or whose unqualified-id names a depen­
    dent type,

  --a cv-qualified type where the unqualified type is dependent,

  --a compound type constructed from any dependent type,

  --an array type constructed from any dependent type or whose  size  is
    specified by a constant expression that is value-dependent,

  --a template-id in which either the template name is a template param­
    eter or any of the template arguments is  a  dependent  type  or  an
    expression that is type-dependent or value-dependent.

  14.6.2.2  Type-dependent expressions                   [temp.dep.expr]

1 Except  as  described  below,  an  expression is type-dependent if any
  subexpression is type-dependent.

2 this is type-dependent if the class type of the enclosing member func­
  tion is dependent (_temp.dep.type_).

3 An id-expression is type-dependent if it contains:

  --an identifier that was declared with a dependent type,

  --a template-id that is dependent,

  --a conversion-function-id that specifies a dependent type,

  --a  nested-name-specifier  that  contains  a  class-name that names a
    dependent type.

4 Expressions of the following forms are type-dependent only if the type
  specified  by  the  type-id,  simple-type-specifier  or new-type-id is
  dependent, even if any subexpression is type-dependent:
          simple-type-specifier ( expression-listopt )
          ::opt new new-placementopt new-type-id new-initializeropt
          ::opt new new-placementopt ( type-id ) new-initializeropt
          dynamic_cast < type-id > ( expression )
          static_cast < type-id > ( expression )
          const_cast < type-id > ( expression )
          reinterpret_cast < type-id > ( expression )
          ( type-id ) cast-expression

5 Expressions of the following forms are never  type-dependent  (because
  the type of the expression cannot be dependent):
          literal
          postfix-expression . pseudo-destructor-name
          postfix-expression -> pseudo-destructor-name
          sizeof unary-expression
          sizeof ( type-id )
          typeid ( expression )
          typeid ( type-id )
          ::opt delete cast-expression
          ::opt delete [ ] cast-expression
          throw assignment-expressionopt

  14.6.2.3  Value-dependent expressions             [temp.dep.constexpr]

1 Except as described below, a constant expression is value-dependent if
  any subexpression is value-dependent.

2 An identifier is value-dependent if it is:

  --a name declared with a dependent type,

  --the name of a non-type template parameter,

  --a constant with integral or enumeration type and is initialized with
    an expression that is value-dependent.

3 Expressions  of  the  following form are value-dependent if the unary-
  expression is type-dependent or the  type-id  is  dependent  (even  if
  sizeof  unary-expression  and  sizeof  ( type-id ) are not type-depen­
  dent):
          sizeof unary-expression
          sizeof ( type-id )

4 Expressions of the following form are value-dependent  if  either  the
  type-id  or  simple-type-specifier  is  dependent or the expression or
  cast-expression is value-dependent:
          simple-type-specifier ( expression-listopt )
          static_cast < type-id > ( expression )
          const_cast < type-id > ( expression )
          reinterpret_cast < type-id > ( expression )
          ( type-id ) cast-expression

  14.6.2.4  Dependent template arguments                 [temp.dep.temp]

1 A template template argument is dependent if it names a template argu­
  ment  or  is a qualified-id where the nested-name-specifier contains a
  class-name that names a dependent type.

2 A non-integral non-type template  argument  is  dependent  if  it  has
  either of the following forms
          qualified-id
          & qualified-id
  and  the  nested-name-specifier  specifies  a  class-name that names a
  dependent type.

3 A type template argument is dependent if  the  type  it  specifies  is
  dependent.

4 An  integral  non-type  template argument is dependent if the constant
  expression it specifies is value-dependent.

  14.6.3  Non-dependent names                              [temp.nondep]

1 Non-dependent names used in a template definition are found using  the
  usual name lookup and bound at the point they are used.  [Example:
          void g(double);
          void h();

          template<class T> class Z {
          public:
                  void f() {
                          g(1); // calls g(double)
                          h++;  // error: cannot increment function
                  }
          };

          void g(int); // not in scope at the point of the template
                       // definition, not considered for the call g(1)
   --end example]

  14.6.4  Dependent name resolution                       [temp.dep.res]

1 In  resolving  dependent  names,  names from the following sources are
  considered:

  --Declarations that are visible at the point of definition of the tem­
    plate.

  --Declarations  from namespaces associated with the types of the func­
    tion arguments both from the  instantiation  context  (_temp.point_)
    and from the definition context.

  14.6.4.1  Point of instantiation                          [temp.point]

1 If  a  function  template  specialization  is  implicitly instantiated
  because it is referenced from a function call that depends on  a  tem­
  plate  argument,  the  point of instantiation of the function template
  specialization is the point of  instantiation  of  the  specialization
  containing the dependent function call.

2 Otherwise, if a function template specialization is implicitly instan­
  tiated because it is referenced within a default argument in a  decla­
  ration,  the  point of instantiation of the function template special­
  ization immediately precedes the namespace scope declaration or  defi­
  nition that refers to the function template specialization.

3 Otherwise,  the point of instantiation of a function template special­
  ization immediately follows the namespace scope declaration or defini­
  tion that refers to the specialization.

  +-------                      BEGIN BOX 7                     -------+
  Gibbons: The wording in previous versions of the working paper put the
  point of instantiation at the reference (even inside a function),  but
  with only namespace-scope names visible.  This was done to ensure that
  the enclosing declaration itself was visible; the end of the enclosing
  declaration  would  have  been  simpler,  but that would have made all
  names injected from within the declaration visible.

4 Now that name injection has been removed, the point  of  instantiation
  can be moved to after the enclosing namespace-scope declaration.

5 N0973R2  (approved  July 96) put the point of instantiation before the
  enclosing declaration.  We think this is wrong, and have corrected it.

6 Yet  another problem is default arguments.  In non-template functions,
  if a default argument tries to use the name of the enclosing function,
  the lookup does not find the name because the end of the declarator of
  the enclosing function has not been reached (i.e. the point of  decla­
  ration).   In  template  functions, if the point of instantiation of a
  function call within a default argument is after the  enclosing  func­
  tion  definition,  the  enclosing  declaration would be in scope.  Not
  only would this be different semantics  for  templates  than  non-tem­
  plates,  but it would require deferring partial lookups of names in of
  default arguments of function templates.

7 So the most consistent approach is to put the point  of  instantiation
  before the enclosing namespace-scope declaration when the reference is
  from a default argument, and after it otherwise.
  +-------                       END BOX 7                      -------+

8 The instantiation context of a function call that depends on the  tem­
  plate arguments is the set of declarations with external linkage visi­
  ble at the point of instantiation of the template specialization  con­
  taining the dependent function call.

  14.6.4.2  Candidate Functions                     [temp.dep.candidate]

1 For  a function call that depends on a template argument, if the func­
  tion name is an unqualified-id,  the  candidate  functions  are  found
  using     the     usual     lookup    rules    (_basic.lookup.unqual_,
  _basic.lookup.koenig_) except that:

  --For  the  part  of  the  lookup  using   unqualified   name   lookup
    (_basic.lookup.unqual_),  only  function  declarations with external
    linkage from the template definition context are found.

  --For  the  part   of   the   lookup   using   associated   namespaces
    (_basic.lookup.koenig_),  only  function  declarations with external
    linkage found in either the template definition context or the  tem­
    plate instantiation context are found.

  If  the  call would be ill-formed or would find a better match had the
  lookup within the associated namespaces considered  all  the  function
  declarations  with  external linkage introduced in those namespaces in
  all translation units, not just considered those declarations found in
  the  template definition and template instantiation contexts, then the
  program has undefined behavior.

  +-------                      BEGIN BOX 8                     -------+
  Gibbons: It might be better to say that if finding a function with  no
  external  linkage  changed  the  semantics, the behavior was also ill-
  formed.  This would make things compatible with implementations  which
  did no hiding at all.
  +-------                       END BOX 8                      -------+

  14.6.4.3  Conversions                                  [temp.dep.conv]

1 Any standard conversion sequence (_over.ics.scs_) may be applied to an
  argument in a function call that depends on a  template  argument.   A
  user-defined  conversion  sequence (_over.ics.user_) may be applied to
  an argument in a function call that depends on  a  template  argument,
  but  the  user-defined  conversion  in this sequence shall either be a
  conversion function that is a member function of the class type of the
  argument, or shall be a constructor of the class type that is the tar­
  get type of the user-defined conversion  sequence.   The  user-defined
  conversion  function  thus  selected shall be found either in the tem­
  plate definition context or in  the  template  instantiation  context.
  [Note:  The set of candidate functions is formed first, before conver­
  sions are considered, so the possible conversions do  not  affect  the
  set of candidate functions.  ]

  14.6.5  Friend names declared within a class             [temp.inject]
       template

1 Friend classes or functions can be declared within a  class  template.
  When  a template is instantiated, the names of its friends are treated
  as if the specialization had been explicitly declared at its point  of
  instantiation.

2 The  names  of friend functions of a class template specialization are
  found by the usual lookup rules, including the  rules  for  associated
  namespaces (_basic.lookup.koenig_).4) [Example:
          template<typename T> class number {
                  //...
                  friend number<T> gcd(const number<T>& x,
                                       const number<T>& y) { ... }
                  //...
          };
          void g()
          {
                  number<double> a, b;
                  //...
                  a = gcd(a,b);   // looks inside number<double> for gcd
          }
   --end example]

  14.7  Template specialization                              [temp.spec]

1 A class instantiated from a class template is called  an  instantiated
  class.   A function instantiated from a function template is called an
  instantiated function.  A  static  data  member  instantiated  from  a
  static data member template is called an instantiated static data mem­
  ber.  The act of instantiating a class, function, or static data  mem­
  ber from a template is referred to as template instantiation.  A class
  declaration introduced by template<> is called an explicitly  special­
  ized  class.   The  name  of the class in such a definition shall be a
  template-id.  A  function  declaration  introduced  by  template<>  is
  called  an  explicitly specialized function.  The name of the function
  in such a declaration may be a template-id.  A static data member dec­
  laration  introduced by template<> is called an explicitly specialized
  static data member.  The name of the class in such a declaration shall
  be a template-id.

  +-------                      BEGIN BOX 9                     -------+
  Corfield:  I  don't  think the above wording is quite right for either
  class member templates or class members of class templates.
  +-------                       END BOX 9                      -------+

  [Example:

  _________________________
  4)  Friend declarations do not introduce new names into any scope, ei­
  ther when the template is declared or when it is instantiated.

          template<class T = int> struct A
          {
                  static int x;
          };
          template<class U> void g(U) { }

          template<> struct A<double> { };  // specialize for T == double
          template<> struct A<> { };        // specialize for T == int
          template<> void g(char) { }       // specialize for U == char
                                            // U is deduced from the parameter type
          template<> void g<int>(int) { }   // specialize for U == int
          template<> int A<char>::x = 0;    // specialize for T == char
          template<> int A<>::x = 1;        // specialize for T == int
   --end example]

2 An instantiated  template  specialization  can  be  either  implicitly
  instantiated  (_temp.inst_) for a given argument list or be explicitly
  instantiated (_temp.explicit_).  A specialization is  a  class,  func­
  tion,  or static data member that is either instantiated or explicitly
  specialized (_temp.expl.spec_).  A template that has been  used  in  a
  way  that  requires a specialization of its definition causes the spe­
  cialization to be implicitly instantiated unless it  has  been  either
  explicitly instantiated or explicitly specialized.

3 No  program  shall explicitly instantiate any template more than once,
  both explicitly instantiate and explicitly specialize a  template,  or
  specialize a template more than once for a given set of template-argu­
  ments.  An implementation is not required to diagnose a  violation  of
  this rule.

4 Each  class  template  specialization instantiated from a template has
  its own copy of any static members.  [Example:
          template<class T> class X {
                  static T s;
                  // ...
          };
          template<class T> T X<T>::s = 0;
          X<int> aa;
          X<char*> bb;
  X<int> has a static member s of type int and  X<char*>  has  a  static
  member s of type char*.  ]

  14.7.1  Implicit instantiation                             [temp.inst]

1 Unless  a  class template specialization has been explicitly instanti­
  ated (_temp.explicit_) or explicitly  specialized  (_temp.expl.spec_),
  the  class template specialization is implicitly instantiated when the
  specialization is referenced in a context that requires a  completely-
  defined  object  type.   Unless a function template specialization has
  been explicitly instantiated or explicitly specialized,  the  function
  template  specialization  is implicitly instantiated when the special­
  ization is referenced in a context that requires a function definition
  to  exist.   Unless  a static data member template has been explicitly
  instantiated  or  explicitly  specialized,  the  static  data   member

  template  specialization  is implicitly instantiated when the special­
  ization is used in a way that requires a  definition  for  the  static
  data member.

2 [Example:
          template<class T> class Z {
          public:
                  void f();
                  void g();
          };
          void h()
          {
                  Z<int> a;     // instantiation of class Z<int> required
                  Z<char>* p;   // instantiation of class Z<char> not
                                // required
                  Z<double>* q; // instantiation of class Z<double>
                                // not required

                  a.f();  // instantiation of Z<int>::f() required
                  p->g(); // instantiation of class Z<char> required, and
                          // instantiation of Z<char>::g() required
          }
  Nothing  in  this  example  requires  class Z<double>, Z<int>::g(), or
  Z<char>::f() to be implicitly instantiated.  ]

3 If a class template for which a definition is in scope is  used  in  a
  way  that involves overload resolution, conversion to a base class, or
  pointer to member conversion, the  class  template  specialization  is
  implicitly instantiated.  [Example:
          template<class T> class B { /* ... */ };
          template<class T> class D : public B<T> { /* ... */ };

          void f(void*);
          void f(B<int>*);

          void g(D<int>* p, D<char>* pp)
          {
                  f(p); // instantiation of D<int> required: call f(B<int>*)

                  B<char>* q = pp; // instantiation of D<char> required:
                                   // convert D<char>* to B<char>*
          }
   --end example]

  +-------                     BEGIN BOX 10                     -------+
  Unruh  believes  the  above paragraph does not precisely enumerate all
  the situations in which templates are required to be instantiated.
  +-------                      END BOX 10                      -------+

4 If an implicit instantiation of a  class  template  specialization  is
  required  and the template is declared but not defined, the program is
  ill-formed.  [Example:

          template<class T> class X;

          X<char> ch; // error: definition of X required
   --end example]

5 If a function template for which a declaration is in scope is used  in
  a  way  that involves overload resolution, a declaration of a function
  template specialization is implicitly instantiated (_temp.over_).

6 An implementation shall not implicitly instantiate  a  function,  non-
  virtual  member  function,  class  or  member  template  that does not
  require instantiation.  It is unspecified whether or not an  implemen­
  tation implicitly instantiates a virtual member function that does not
  require specialization.

7 Implicitly instantiated class template, function, and static data mem­
  ber specializations are placed in the namespace where the template was
  defined.  [Example:
          namespace N {
                  template<class T> class List {
                  public:
                          T* get();
                          // ...
                  };
          }
          template<class K, class V> class Map {
                  N::List<V> lt;
                  V get(K);
                  //  ...
          };
          void g(Map<char*,int>& m)
          {
                  int i = m.get("Nicholas");
                  // ...
          }
  a  call   of   lt.get()   from   Map<char*,int>::get()   would   place
  List<int>::get()  in  the namespace N rather than in the global names­
  pace.  ]

8 [Note: _temp.point_ defines the point of instantiation of  a  template
  specialization.  ]

9 If a virtual function is implicitly instantiated, its point of instan­
  tiation is immediately following the point of  instantiation  for  its
  class.

10The point of instantiation for a template used inside another template
  and not instantiated previous to an  instantiation  of  the  enclosing
  template  is  immediately  before  the  point  of instantiation of the
  enclosing template.

11There is an implementation-defined quantity that specifies  the  limit
  on  the  depth of recursive instantiations.  The result of an infinite
  recursion in instantiation is undefined.  [Example:

          template<class T> class X {
                  X<T>* p; // ok
                  X<T*> a; // implicit generation of X<T> requires
                           // the implicit instantiation of X<T*> which requires
                           // the implicit instantiation of X<T**> which ...
          };
   --end example]

  14.7.2  Explicit instantiation                         [temp.explicit]

1 A  class, function or static data member specialization can be explic­
  itly instantiated from its template.

2 The syntax for explicit instantiation is:
          explicit-instantiation:
                  template declaration
  where the unqualified-id in the declaration shall  be  either  a  tem­
  plate-id  or, where all template arguments can be deduced, a template-
  name.  [Note: the declaration may declare  a  qualified-id,  in  which
  case  the unqualified-id of the qualified-id must be a template-id.  ]
  [Example:
          template<class T> class Array { /* ... */ };
          template class Array<char>;

          template<class T> void sort(Array<T>& v) { /* ... */ }
          template void sort(Array<char>&); // argument is deduced here

          namespace N {
                  template<class T> void f(T&) { }
          }
          template void N::f<int>(int&);
   --end example]

3 A declaration of a function template shall be in scope at the point of
  an  explicit  instantiation of the function template.  A definition of
  the class template shall be in scope at  the  point  of  the  explicit
  instantiation of the class template.  A declaration of the static data
  member template shall be in scope at the point of the explicit instan­
  tiation  of the static data member template.  If the declaration names
  a compiler-generated function, the program is ill-formed.

4 The definition of a non-exported  function  template  or  non-exported
  data  member  template  shall  be present in every translation unit in
  which it is explicitly instantiated.

  +-------                     BEGIN BOX 11                     -------+
  Unruh: should explicit instantiation define exactly one  instantiation
  point?   Corfield:  this  depends  on the specification chosen for the
  template compilation model - in particular, if explicit  instantiation
  defines  exactly  one  instantiation  point,  what impact would be the
  impact of removing separate compilation of templates (i.e., how  would
  an implementation know where the single instantiation point was?).
  +-------                      END BOX 11                      -------+

5 An explicit instantiation of a template specialization is in the scope
  of the namespace in which the template was defined.  [Example:
          namespace N {
                  template<class T> class Y { /* ... */ };
          }

          template class Y<int>; // error: class template Y not visible
                                 // in the global namespace

          using N::Y;
          template class Y<int>; // ok: explicit instantiation in namespace N

          template class N::Y<char*>; // ok: explicit instantiation in namespace N
   --end example]

6 A trailing template-argument can be left unspecified  in  an  explicit
  instantiation of a function template specialization provided it can be
  deduced from the function argument type (_temp.deduct_).  [Example:
          template<class T> class Array { /* ... */ };
          template<class T> void sort(Array<T>& v);

          // instantiate sort(Array<int>&) - template-argument deduced
          template void sort<>(Array<int>&);
   --end example]

7 The explicit instantiation of a class template specialization  implies
  the instantiation of all of its members not previously explicitly spe­
  cialized in the translation unit containing  the  explicit  instantia­
  tion.   A member class of a class template may be explicitly instanti­
  ated.

8 The usual access checking rules do not apply  to  explicit  instantia­
  tions.  [Note: In particular, the template arguments and names used in
  the function declarator (including parameter types, return  types  and
  exception  specifications) may be private types or objects which would
  normally not be accessible and the template may be a  member  template
  or member function which would not normally be accessible.  ]

  14.7.3  Explicit specialization                       [temp.expl.spec]

1 An explicit specialization of any of the following:

  --function template

  --class template

  --member function of a class template

  --static data member of a class template

  --member class of a class template

  --member class template of a class template

  --member function template of a class template

  can be declared by a declaration introduced by template<>; that is:
          specialization:
                  template < > declaration
  [Example:
          template<class T> class stream;

          template<> class stream<char> { /* ... */ };
          template<class T> class Array { /* ... */ };
          template<class T> void sort(Array<T>& v) { /* ... */ }

          template<> void sort<char*>(Array<char*>&) ;
  Given  these declarations, stream<char> will be used as the definition
  of streams of chars; other streams will be handled by  class  template
  specializations  instantiated  from  the  class  template.  Similarly,
  sort<char*> will be used as the sort function for  arguments  of  type
  Array<char*>;  other Array types will be sorted by functions generated
  from the template.  ]

2 An explicit specialization must be declared in the namespace of  which
  it  is  a member, or, for class members, in the namespace of which the
  class is a member.  Such a declaration may also be a  definition.   If
  the declaration is not a definition, the specialization may be defined
  later in the  namespace  in  which  the  explicit  specialization  was
  declared,  or  in  a  namespace  that  encloses  the  one in which the
  explicit specialization was declared.

3 Default function arguments shall not be specified in a declaration  or
  a definition of an explicit specialization.

4 A declaration of the template being explicitly specialized shall be in
  scope at the point of declaration of an explicit  specialization.   If
  the  declaration  names  a implicitly-declared special member function
  (_special_), the program is ill-formed.  [Note: a declaration, but not
  a definition of the template is required.  ] [Example:
          template<> class X<int> { /* ... */ }; // error: X not a template

          template<class T> class X;

          template<> class X<char*> { /* ... */ }; // fine: X is a template
   --end example]

5 If a template is explicitly specialized then that specialization shall
  be declared before the first use of  that  specialization  that  would
  cause  an  implicit  instantiation to take place, in every translation
  unit in which such a use occurs.  [Example:

          template<class T> class Array { /* ... */ };
          template<class T> void sort(Array<T>& v) { /* ... */ }

          void f(Array<String>& v)
          {
                  sort(v); // use primary template
                           // sort(Array<T>&), T is String
          }

          template<> void sort<String>(Array<String>& v); // error: specialization
                                                   // after use of primary template
          template<> void sort<>(Array<char*>& v); // fine sort<char*> not yet used
   --end example] If a function, class or static  data  member  template
  has  been explicitly specialized for a template-argument-list, no spe­
  cialization shall be implicitly instantiated for  that  template-argu­
  ment-list.

6 A template explicit specialization is in the scope of the namespace in
  which the template was defined.  [Example:
          namespace N {
                  template<class T> class X { /* ... */ };
                  template<class T> class Y { /* ... */ };

                  template<> class X<int> { /* ... */ }; // ok: specialization
                                                         //     in same namespace
                  template<> class Y<double>;            // forward declare intent to
                                                         // specialize for double
          }

          template<> class N::Y<double> { /* ... */ }; // ok: specialization
                                                       //     in same namespace
   --end example]

7 A template-id that names a class template explicit specialization that
  has  been  declared but not defined can be used exactly like the names
  of other incompletely-defined classes (_basic.types_).  [Example:
          template<class T> class X; // X is a class template
          template<> class X<int>;

          X<int>* p; // ok: pointer to declared class X<int>
          X<int> x; // error: object of incomplete class X<int>
   --end example]

8 A trailing template-argument can be left unspecified  in  an  explicit
  function  template  specialization provided it can be deduced from the
  function argument type.  [Example:
          template<class T> class Array { /* ... */ };
          template<class T> void sort(Array<T>& v);

          // explicit specialization for sort(Array<int>&)
          // with deduces template-argument of type int
          template<> void sort(Array<int>&);
   --end example]

9 It is possible for a specialization with a given function signature to
  be  instantiated from more than one function template.  In such cases,
  explicit specification of the  template  arguments  must  be  used  to
  uniquely  identify the function template specialization being special­
  ized.  [Example:
          template <class T> void f(T);
          template <class T> void f(T*);
          template <>        void f(int*);        // Ambiguous
          template <>        void f<int>(int*);   // OK
          template <>        void f(int);         // OK
   --end example]

10A function with the same name as a template and a  type  that  exactly
  matches  that of a template specialization is not an explicit special­
  ization (_temp.fct_).

11An explicit specialization of a function template is inline only if it
  is  explicitly  declared to be, and independently of whether its func­
  tion template is.  [Example:
          template<class T> void f(T) { /* ... */ }
          template<class T> inline T g(T) { /* ... */ }

          template<> inline void f<>(int) { /* ... */ } // ok: inline
          template<> int g<>(int) { /* ... */ } // ok: not inline
   --end example]

12Member function templates,  member  class  templates  of  non-template
  classes  and  class template specializations may be specialized in the
  same manner as function templates and class templates.

13A specialization of a member function template or  member  class  tem­
  plate of a non-specialized class template is itself a template.

14An  explicit specialization of a static data member of a template is a
  definition if the declaration includes an initializer;  otherwise,  it
  is  a  declaration.  [Note: there is no syntax for the definition of a
  static data member of a template that requires default initialization.
          template<> X Q<int>::x;
  This  is a declaration regardless of whether X can be default initial­
  ized (_dcl.init_).  ]

15A member template of a class template may  be  explicitly  specialized
  for  a given implicit instantiation of the class template, even if the
  member template is defined  in  the  class  template  definition.   An
  explicit  specialization  of  a member template is specified using the
  template specialization syntax.  Default function arguments shall  not
  be supplied in such declarations.  [Example:

          template<class T> struct A {
                  void f(T);
                  template<class X> void g(T,X);
                  void h(T) { }
          };

          // specialization
          template<> void A<int>::f(int);

          // out of class member template definition
          template<class T> template<class X> void A<T>::g(T,X) { }
          // member template partial specialization
          template<> template<class X> void A<int>::g(int,X);

          // member template specialization
          template<> template<>
                  void A<int>::g(int,char);        // X deduced as char
          template<> template<>
                  void A<int>::g<char>(int,char);  // X specified as char

          // member specialization even if defined in class definition
          template<> void A<int>::h(int) { }
   --end example]

16A member template of an explicitly specialized class is not be implic­
  itly instantiated from the general template.  Instead, the member tem­
  plate shall itself be explicitly specialized.  [Example:
          template<class T> struct A {
                  void f(T) { /* ... */ }
          };

          template<> struct A<int> {
                  void f(int);
          };
          void h()
          {
                  A<int> a;
                  a.f(16);  // A<int>::f must be defined somewhere
          }

          template<> void A<int>::f() { /* ... */ }
    --end  example] The definition of an explicitly specialized class is
  unrelated to the definition of a generated specialization.   That  is,
  its  members  need not have the same names, types, etc. as the members
  of the a generated  specialization.   Definitions  of  members  of  an
  explicitly specialized class are defined in the same manner as members
  of normal classes, and not using the explicit specialization syntax.

17An explicit specialization declaration shall not be a friend  declara­
  tion.

  14.8  Function template specializations                [temp.fct.spec]

1 A  function instantiated from a function template is called a function
  template specialization; so is an explicit specialization of  a  func­
  tion  template.  Template arguments can either be explicitly specified
  in a call or be deduced (_temp.deduct_) from the function arguments.

2 Each function template instantiated from a template has its  own  copy
  of any static variable.  [Example:
          template<class T> f(T* p)
          {
                  static T s;
                  // ...
          };

          void g(int a, char* b)
          {
                  f(&a);  // call f<int>(int*)
                  f(&b);  // call f<char*>(char**)
          }
  Here   f<int>(int*)   has   a  static  variable  s  of  type  int  and
  f<char*>(char**) has a static variable s of type char*.  ]

  14.8.1  Explicit template argument                 [temp.arg.explicit]
       specification

1 Template  arguments can be specified in a call by qualifying the func­
  tion template specialization name by the  list  of  template-arguments
  exactly  as  template-arguments  are specified in uses of a class tem­
  plate specialization.  [Example:
          template<class T> void sort(Array<T>& v);
          void f(Array<dcomplex>& cv, Array<int>& ci)
          {
                  sort<dcomplex>(cv); // sort(Array<dcomplex>&)
                  sort<int>(ci);      // sort(Array<int>&)
          }
  and
          template<class U, class V> U convert(V v);

          void g(double d)
          {
                  int i = convert<int,double>(d);  // int convert(double)
                  char c = convert<char,double>(d); // char convert(double)
          }
   --end example]

2 Trailing arguments that can be deduced (_temp.deduct_) may be  omitted
  from the list of explicit template-arguments.  [Example:
          template<class X, class Y> X f(Y);
          void g()
          {
                  int i = f<int>(5.6); // Y is deduced to be double
                  int j = f(5.6);      // ill-formed: X cannot be deduced
          }

   --end example]

3 Implicit conversions (_conv_) will be performed on a function argument
  to bring it to the type of the corresponding function parameter if the
  parameter  type  is  fixed by an explicit specification of a template-
  argument.  [Example:
          template<class T> void f(T);

          class Complex {
                  // ...
                  Complex(double);
          };

          void g()
          {
                  f<Complex>(1); // ok, means f<Complex>(Complex(1))
          }
   --end example]

4 [Note: because the explicit template argument list follows  the  func­
  tion  template  name, and because conversion member function templates
  and constructor member function templates are called without  using  a
  function  name,  there is no way to provide an explicit template argu­
  ment list for these function templates.  ]

  14.8.2  Template argument deduction                      [temp.deduct]

1 Template arguments that can be deduced from the function arguments  of
  a call need not be explicitly specified.  [Example:
          void f(Array<dcomplex>& cv, Array<int>& ci)
          {
                  sort(cv);   // call sort(Array<dcomplex>&)
                  sort(ci);   // call sort(Array<int>&)
          }
  and
          void g(double d)
          {
                  int i = convert<int>(d);   // call convert<int,double>(double)
                  int c = convert<char>(d);  // call convert<char,double>(double)
          }
    --end example] [Note: if a template-parameter is only used to repre­
  sent a function template return type, its corresponding template-argu­
  ment  cannot  be  deduced and the template-argument must be explicitly
  specified.  ]

2 Type deduction is done for each function template argument that is not
  explicitly  specified.  The type of the parameter of the function tem­
  plate (call it P) is compared to the type of the  corresponding  argu­
  ment  of  the  call (call it A), and an attempt is made to find a type
  for the template type argument, a template for the  template  template
  argument or a value for the template non-type argument, that will make
  P after substitution of the deduced  type  or  value  (call  that  the
  deduced  A) compatible with the call argument.  Type deduction is done
  independently  for  each  parameter/argument  pair,  and  the  deduced

  template  argument  types, templates and values are then combined.  If
  type deduction cannot be done for any parameter/argument pair,  or  if
  for  any  parameter/argument pair the deduction leads to more than one
  possible set of deduced types, templates or values,  or  if  different
  parameter/argument  pairs  yield different deduced types, templates or
  values for a given template argument,  or  if  any  template  argument
  remains  neither  deduced  nor explicitly specified, template argument
  deduction fails.

3 If P is not a reference type:

  --if A is an array type, the pointer type produced  by  the  array-to-
    pointer standard conversion (_conv.array_) is used in place of A for
    type deduction; otherwise,

  --if A is a function type, the pointer type produced by the  function-
    to-pointer  standard  conversion (_conv.func_) is used in place of A
    for type deduction; otherwise,

  --if A is a cv-qualified type, the top level cv-qualifiers of A's type
    are ignored for type deduction.

  If  P  is a cv-qualified type, the top level cv-qualifiers of P's type
  are ignored for type deduction.  If P is a reference  type,  the  type
  referred to by P is used in place of P for type deduction.

4 In  general,  the deduction process attempts to find template argument
  values that will make the deduced A identical to A (after the  type  A
  is  transformed  as  described above).  However, there are three cases
  that allow a difference:

  --If the original P is a reference type, the deduced A (i.e., the type
    referred to by the reference) can be more cv-qualified than A.

  --If  P  is  a  pointer  or  pointer  to member type, A can be another
    pointer or pointer to member type  that  can  be  converted  to  the
    deduced A via a qualification conversion (_conv.qual_).

  --If  P is a class, and P has the form class-template-name<arguments>,
    A can be a derived class of the deduced A.   Likewise,  if  P  is  a
    pointer to a class of the form class-template-name<arguments>, A can
    be a pointer to a derived class pointed to by the deduced A.

  These alternatives are considered only if  type  deduction  cannot  be
  done  otherwise.   If they yield more than one possible deduced A, the
  type deduction fails.  When deducing arguments in the context of  tak­
  ing the address of an overloaded function (_over.over_), these inexact
  deductions are not considered.

5 [Example: here is an example  in  which  different  parameter/argument
  pairs produce inconsistent template argument deductions:

          template<class T> void f(T x, T y) { /* ... */ }
          struct A { /* ... */ };
          struct B : A { /* ... */ };
          int g(A a, B b)
          {
                  f(a,b);  // error: T could be A or B
                  f(b,a);  // error: T could be A or B
                  f(a,a);  // ok: T is A
                  f(b,b);  // ok: T is B
          }

6 Here  is  an  example  where two template arguments are deduced from a
  single function parameter/argument pair.  This can lead  to  conflicts
  that cause type deduction to fail:
          template <class T, class U> void f(  T (*)( T, U, U )  );

          int g1( int, float, float);
          char g2( int, float, float);
          int g3( int, char, float);

          void r()
          {

                  f(g1);          // ok: T is int and U is float
                  f(g2);          // error: T could be char or int
                  f(g3);          // error: U could be char or float
          }

7 Here  is  an  example where a qualification conversion applies between
  the argument type on the function call and the deduced template  argu­
  ment type:
          template<class T> void f(const T*) {}
          int *p;
          void s()
          {
                  f(p);  // f(const int *)
          }

8 Here  is an example where the template argument is used to instantiate
  a derived class type of the corresponding function parameter type:
          template <class T> struct B { };
          template <class T> struct D : public B<T> {};
          struct D2 : public B<int> {};
          template <class T> void f(B<T>&){}
          void t()
          {
                  D<int> d;
                  D2     d2;
                  f(d);  // calls f(B<int>&)
                  f(d2); // calls f(B<int>&)
          }
   --end example]

9 A template type argument T, a template template argument TT or a  tem­
  plate  non-type  argument  i can be deduced if P and A have one of the
  following forms:
          T
          cv-list T
          T*
          T&
          T[integer-constant]
          class-template-name<T>
          type(*)(T)
          T(*)()
          T(*)(T)
          type T::*
          T type::*
          T (type::*)()
          type (T::*)()
          type (type::*)(T)
          type[i]
          class-template-name<i>
          TT<T>
          TT<i>
          TT<>
  where (T) represents argument lists where at least one  argument  type
  contains a T, and () represents argument lists where no parameter con­
  tains a T.  Similarly, <T> represents template argument lists where at
  least  one  argument  contains  a  T, <i> represents template argument
  lists where at least one argument contains an i and <> represents tem­
  plate argument lists where no argument contains a T or an i.

10In  a  type  which contains a nested-name-specifier, template argument
  values cannot be deduced  for  template  parameters  used  within  the
  nested-name-specifier.  [Example:
          template<int i, typename T>
          T deduce(A<T>::X x,     // T is not deduced here
                   T       t,     // but T is deduced here
                   B<i>::Y y);    // i is not deduced here
          A<int> a;
          B<77>  b;
          int    x = deduce<77>(a.xm, 62, y.ym);
          // T is deduced to be int, a.xm must be convertible to
          // A<int>::X
          // i is explicitly specified to be 77, y.ym must be convertible
          // to B<77>::Y
    --end example] When a template parameter is used in this context, an
  argument value that has been explicitly  specified,  or  deduced  from
  other  arguments  is  used.  If the value cannot be deduced elsewhere,
  and is not explicitly specified, the program is  ill-formed.   Conver­
  sions  (_conv_)  will  be performed on a function argument that corre­
  sponds with a function parameter that contains only non-deducible tem­
  plate   parameters   and   explicitly  specified  template  parameters
  (_temp.arg.explicit_).

  +-------                     BEGIN BOX 12                     -------+
  Corfield: the permissible forms need to be reviewed - the list is  not

  complete and is not a particularly useful  way  to  decide  whether  a
  given form is allowed, despite the following text about composition of
  types.
  +-------                      END BOX 12                      -------+

  These forms can be used in the same way as T is for  further  composi­
  tion of types.  [Example:
          X<int> (*)(char[6])
  is of the form
          class-template-name<T> (*)(type[i])
  which is a variant of
          type (*)(T)
  where type is X<int> and T is char[6].  ]

11Template arguments cannot be deduced from function arguments involving
  constructs other than the ones specified above.

12A template type argument cannot be deduced from the type of a non-type
  template-argument.  [Example:
          template<class T, T i> void f(double a[10][i]);
          int v[10][20];
          f(v); // error: argument for template-parameter T cannot be deduced
   --end example]

13[Note:  except for reference and pointer types, a major array bound is
  not part of a function parameter type and cannot be  deduced  from  an
  argument:
          template<int i> void f1(int a[10][i]);
          template<int i> void f2(int a[i][20]);
          template<int i> void f3(int (&a)[i][20]);
          void g()
          {
                  int v[10][20];
                  f1(v);     // ok: i deduced to be 20
                  f1<20>(v); // ok
                  f2(v);     // error: cannot deduce template-argument i
                  f2<10>(v); // ok
                  f3(v);     // ok: i deduced to be 10
          }
   --end note]

14If,  in  the  declaration  of a function template with a non-type tem­
  plate-parameter, the non-type template-parameter is used in an expres­
  sion  in the function parameter-list, the corresponding template-argu­
  ment shall always be explicitly specified because type deduction would
  otherwise always fail for such a template-argument.  [Example:
          template<int i> class A { /* ... */ };
          template<short s> void g(A<s+1>);
          void k() {
            A<1> a;
            g(a);       // error: deduction fails for expression s+1
            g<0>(a);    // ok
          }
   --end example]

15If,  in  the  declaration  of a function template with a non-type tem­
  plate-parameter, the non-type template-parameter is used in an expres­
  sion  in  the  function  parameter-list and, if the corresponding tem­
  plate-argument is deduced, the template-argument type shall match  the
  type  of  the template-parameter exactly, except that a template-argu­
  ment deduced from an array bound may be of any integral type.5) [Exam­
  ple:
          template<int i> class A { /* ... */ };
          template<short s> void f(A<s>);
          void k1() {
            A<1> a;
            f(a);       // error: deduction fails for conversion from int to short
            f<1>(a);    // ok
          }
          template<const short cs> class B { };
          template<short s> void h(B<s>);
          void k2() {
            B<1> b;
            g(b);       // ok: cv-qualifiers are ignored on template parameter types
          }
   --end example]

16A  template-argument  can  be  deduced  from  a pointer to function or
  pointer to member function argument if the set of overloaded functions
  does  not contain function templates and at most one of a set of over­
  loaded functions provides a unique match.  [Example:
          template<class T> void f(void(*)(T,int));
          template<class T> void foo(T,int);
          void g(int,int);
          void g(char,int);
          void h(int,int,int);
          void h(char,int);
          int m()
          {
                  f(&g);    // error: ambiguous
                  f(&h);    // ok: void h(char,int) is a unique match
                  f(&foo);  // error: type deduction fails because foo is a template
          }
   --end example]

17If function template-arguments are explicitly  specified  in  a  call,
  they  shall  be  specified in declaration order of their corresponding
  template-parameters.  Trailing arguments can be left out of a list  of
  explicit template-arguments.  [Example:

  _________________________
  5) Although the template-argument corresponding to a  template-parame­
  ter  of  type  bool  may be deduced from an array bound, the resulting
  value will always be true because the array bound will be non-zero.

  template<class X, class Y, class Z> X f(Y,Z);
          void g()
          {
                  f<int,char*,double>("aa",3.0);
                  f<int,char*>("aa",3.0); // Z is deduced to be double
                  f<int>("aa",3.0);       // Y is deduced to be char*, and
                                          // Z is deduced to be double
                  f("aa",3.0);            // error: X cannot be deduced
          }
   --end example]

18A  template  type-parameter cannot be deduced from the type of a func­
  tion default argument.  [Example:
          template <class T> void f(T = 5, T = 7);
          void g()
          {
                  f(1);     // ok: call f<int>(1,7)
                  f();      // error: cannot deduce T
                  f<int>(); // ok: call f<int>(5,7)
          }
   --end example]

19The template-argument corresponding to a  template  template-parameter
  is  deduced from the type of the template-argument of a class template
  specialization used in the argument list of a function  call.   [Exam­
  ple:
          template <template X<class T> > struct A { };
          template <template X<class T> > void f(A<X>) { }
          template<class T> struct B { };
          A<B> ab;
          f(ab); // calls f(A<B>)
   --end example]

20If trailing template-arguments are left unspecified in a function tem­
  plate    explicit    instantiation    or    explicit    specialization
  (_temp.explicit_,  _temp.expl.spec_),  the  template  arguments can be
  deduced from the function parameters according to the rules  specified
  in this subclause.  [Note: a default template-argument cannot be spec­
  ified in a function  template  declaration  or  definition;  therefore
  default  template-arguments cannot be used to influence template argu­
  ment deduction.  ]

  14.8.3  Overload resolution                                [temp.over]

1 A function template can be overloaded either by  (non-template)  func­
  tions  of its name or by (other) function templates of that same name.
  When a call to that name is written (explicitly, or  implicitly  using
  the operator notation), template argument deduction (_temp.deduct_) is
  performed for each function template to  find  the  template  argument
  values  (if  any)  that  can  be  used  with that function template to
  instantiate a function template specialization  that  can  be  invoked
  with  the call arguments.  For each function template, if the argument
  deduction succeeds, the deduced template-arguments are used to instan­
  tiate  a single function template specialization which is added to the

  candidate functions set to be used in overload resolution.  If, for  a
  given function template, argument deduction fails, no such function is
  added to the set of candidate functions for that template.   The  com­
  plete  set  of candidate functions includes all the function templates
  instantiated in this way and all of the non-template overloaded  func­
  tions  of  the  same  name.  The function template specializations are
  treated like any other functions in the remainder of overload  resolu­
  tion, except as explicitly noted.6)

2 [Example:
          template<class T> T max(T a, T b) { return a>b?a:b; };

          void f(int a, int b, char c, char d)
          {
                  int m1 = max(a,b);  // max(int a, int b)
                  char m2 = max(c,d); // max(char a, char b)
                  int m3 = max(a,c);  // error: cannot generate max(int,char)
          }

3 Adding
          int max(int,int);
  to  the  example  above  would  resolve the third call, by providing a
  function that could be called for max(a,c) after  using  the  standard
  conversion of char to int for c.

4 Here  is  an  example  involving  conversions  on  a function argument
  involved in template-argument deduction:
          template<class T> struct B { /* ... */ };
          template<class T> struct D : public B<T> { /* ... */ };
          template<class T> void f(B<T>&);
          void g(B<int>& bi, D<int>& di)
          {
                  f(bi);  // f(bi)
                  f(di);  // f( (B<int>&)di )
          }

5 Here is an example involving conversions on a  function  argument  not
  involved in template-parameter deduction:
          template<class T> void f(T*,int);  // #1
          template<class T> void f(T,char);  // #2

  _________________________
  6) The parameters of function template specializations contain no tem­
  plate parameter types.  The set of conversions allowed on deduced  ar­
  guments  is  limited,  because the argument deduction process produces
  function templates with parameters that either match  the  call  argu­
  ments  exactly  or  differ only in ways that can be bridged by the al­
  lowed limited conversions.  Non-deduced arguments allow the full range
  of conversions.

          void h(int* pi, int i, char c)
          {
                  f(pi,i);  // #1: f<int>(pi,i)
                  f(pi,c);  // #2: f<int*>(pi,c)

                  f(i,c);   // #2: f<int>(i,c);
                  f(i,i);   // #2: f<int>(i,char(i))
          }
   --end example]

6 Only  the signature of a function template specialization is needed to
  enter the specialization in a set of candidate  functions.   Therefore
  only the function template declaration is needed to resolve a call for
  which a template specialization is a candidate.  [Example:
          template<class T> void f(T);    // declaration

          void g()
          {
                  f("Annemarie"); // call of f<const char*>
          }
  The call of f is well-formed even if the template f is  only  declared
  and  not  defined  at the point of the call.  The program will be ill-
  formed unless a specialization for f<const char*>,  either  implicitly
  or explicitly generated, is present in some translation unit.  ]