US263 23.03.4.2 Make shared_ptr<int>& satisfy readable LWG 3279 P1878

[wg21bot]

In the current spec, shared_ptr<int> is readable, but shared_ptr<int>& is not. That is because readable_traits is not stripping top-level references before testing for nested typedefs.

Proposed change:
Change every occurance of iter_value_t<In> in the definition of the readable concept with iter_value_t<remove_reference_t<In>>.

See https://cplusplus.github.io/LWG/issue3279

[JeffGarland]

Reviewed P1878 and adopted by large group on Wed in Belfast.

straw polls to adopt for C++20
F N A
13 0 1

[jensmaurer]

Accepted with modification. See paper P1878R1.