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### 2387. More nested types that must be accessible and unambiguous

Section: 22.10.4 [func.require], 22.10.6 [refwrap] Status: C++17 Submitter: Jonathan Wakely Opened: 2014-05-23 Last modified: 2017-07-30

Priority: Not Prioritized

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Discussion:

Further to 2299 and 2361, 22.10.4 [func.require] p3 and 22.10.6 [refwrap] p3 and p4 talk about member types without any mention of being accessible and unambiguous.

[2014-06-05 Daniel provides wording]

[2014-06-06 Library reflector vote]

The issue has been identified as Tentatively Ready based on six votes in favour.

Proposed resolution:

This wording is relative to N3936.

1. Change 22.10.4 [func.require] p3 as indicated:

   > -3- If a call wrapper (20.9.1) has a weak result type the type of its member type `result_type` is based on the type `T` of the wrapper's target object (20.9.1):

   > - if `T` is a pointer to function type, `result_type` shall be a synonym for the return type of `T`;

   > - if `T` is a pointer to member function, `result_type` shall be a synonym for the return type of `T`;

   > - if `T` is a class type and the qualified-id `T::result_type` is valid and denotes a type (13.10.3 [temp.deduct])with a member type `result_type`, then `result_type` shall be a synonym for `T::result_type`;

   > - otherwise `result_type` shall not be defined.

2. Change 22.10.6 [refwrap] p3+p4 as indicated:

   > -3- The template instantiation `reference_wrapper<T>` shall define a nested type named `argument_type` as a synonym for `T1` only if the type `T` is any of the following:

   > - a function type or a pointer to function type taking one argument of type `T1`

   > - a pointer to member function `R T0::f` cv (where cv represents the member function_s cv-qualifiers); the type `T1` is cv `T0*`

   > - a class type where the qualified-id `T::argument_type` is valid and denotes a type (13.10.3 [temp.deduct])with a member type `argument_type`; the type `T1` is `T::argument_type`.

   > -4- The template instantiation `reference_wrapper<T>` shall define two nested types named `first_argument_type` and `second_argument_type` as synonyms for `T1` and `T2`, respectively, only if the type `T` is any of the following:

   > - a function type or a pointer to function type taking two arguments of types `T1` and `T2`

   > - a pointer to member function `R T0::f(T2)` cv (where cv represents the member function's cv-qualifiers); the type `T1` is cv `T0*`

   > - a class type where the qualified-ids `T::first_argument_type` and `T::second_argument_type` are both valid and both denote types (13.10.3 [temp.deduct])with member types `first_argument_type` and `second_argument_type`; the type `T1` is `T::first_argument_type`. and the type `T2` is `T::second_argument_type`.