Jens Maurer
N3277=11-0047
2011-03-25

N3277: Core issues 1194/1195/1199: References and constexpr

This paper presents the changes necessary to resolve core issues 1194 "Constexpr references", 1195 "References to non-literal types in constexpr functions", and 1199 "Deleted constexpr functions".

Change in 3.9 basic.types paragraph 10:

A type is a literal type if it is:

a scalar type; or

a reference type; or

...

Change in 5.19 expr.const paragraph 1:

an lvalue-to-rvalue conversion (4.1 conv.lval) unless it is applied to

...

a glvalue of literal type that refers to a non-volatile temporary object whose lifetime has not ended, initialized with a constant expression; ~~[ Footnote: ... ]~~

an id-expression that refers to a variable or data member of reference type unless the reference has a preceding initialization, initialized with a constant expression ~~[ Footnote: ... ]~~;

Change in 7.1.5 dcl.constexpr paragraph 1:

The constexpr specifier shall be applied only to the definition of ~~an object~~ a variable, the declaration of a function or function template, or the declaration of a static data member of a literal type (3.9 basic.types). ...

Change in 7.1.5 dcl.constexpr paragraph 3:

...

its return type shall be a literal type ~~or a reference to literal type~~

each of its parameter types shall be a literal type ~~or a reference to literal type~~
its function-body shall be = delete or a compound-statement of the form
    { return expression ; }
...

Change in 7.1.5 dcl.constexpr paragraph 4:

In a definition of a constexpr constructor, each of the parameter types shall be a literal type. In addition, either its function-body shall be = delete or it ~~The definition of a constexpr constructor~~ shall satisfy the following constraints:

~~each of its parameter types shall be a literal type or a reference to literal type;~~

...

Change in 7.1.5 dcl.constexpr paragraph 8:

A constexpr specifier used in an object declaration declares the object as const. Such an object shall be initialized. If it is initialized by a constructor call, the constructor shall be a constexpr constructor and every argument to the constructor shall be a constant expression. Otherwise, or if a constexpr specifier is used in a reference declaration, every full-expression that appears in its initializer shall be a constant expression.