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3200. midpoint should not constrain T is complete

Section: 27.10.16 [numeric.ops.midpoint] Status: C++20 Submitter: Paolo Torres Opened: 2019-04-10 Last modified: 2021-02-25

Priority: 2

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Discussion:

The constraint of the midpoint overload in 27.10.16 [numeric.ops.midpoint]:

template<class T>
constexpr T* midpoint(T* a, T* b);

-4- Constraints: T is a complete object type.

is incorrect. Paragraph 4 states T is constrained to be a complete object type, however it does not seem to be possible to implement T is complete. This means behavior is conditioned dependent on whether a type is complete, and this seems inconsistent with the library precedent.

[2019-06-12 Priority set to 2 after reflector discussion]

[2020-02 Status to Immediate on Thursday night in Prague.]

Proposed resolution:

This wording is relative to N4810.

1. Modify 27.10.16 [numeric.ops.midpoint] as indicated:

   template<class T>
     constexpr T* midpoint(T* a, T* b);
   

   -4- Constraints: T is an complete object type.

   -?- Mandates: T is a complete type.

   […]