1. Revision History
1.1. Revision 1 - November 7th, 2018
Add Tony Table and fix the example in the Tony Table.
1.2. Revision 0 - October 7th, 2018
attribute has helped prevent a serious class of software bugs, but sometimes it is hard to communicate exactly why a function is marked as
This paper adds an addendum to allow a person to add a string attribute token to let someone provide a small reasoning or reminder for why a function has been marked
3. Design Considerations
This paper is an enhancement of a preexisting feature to help programmers provide clarity with their code. Anything that makes the implementation warn or error should also provide some reasoning or perhaps point users to a knowledge base or similar to have any questions they have about the reason for the
The design is very simple and follows the lead of the
attribute. We propose allowing a string literal to be passed as an attribute argument clause, allowing for
. The key here is that there are some
attributes that have different kinds of "severity" versus others. That is, the cost of discarding
's return value is probably of slightly less concern than
: one might manifest as a possible bug, the other is a downright memory leak.
Adding a reason to
allows implementers of the standard library, library developers, and application writers to benefit from a more clear and concise error beyond "Please do not discard this return value". This makes it easier for developers to understand the intent of the code they are using.
All wording is relative to [n4762].
The intent of the wording is to let a programmer specify a string literal that the compiler can use in their warning / error display for, e.g.
4.2. Feature Test Macro
already has an attribute value in Table 15. If this proposal is accepted, then per the standard’s reasoning the value of
should be increased to some greater value (such as
4.3. Proposed Wording
Modify §14.1 [cpp.cond]'s Table 15:
Attribute Value nodiscard 201603L
Append the following to §9.11.9 Nodiscard attribute [dcl.attr.nodiscard]'s clause 1:
1 The attribute-token nodiscard may be applied to the declarator-id in a function declaration or to the declaration of a class or enumeration. It shall appear at most once in each attribute-list and no attribute argument-clause shall be present.