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### 3279. `shared_ptr<int>&` does not not satisfy `readable`

Section: 25.3.4.2 [iterator.concept.readable] Status: Resolved Submitter: Eric Niebler Opened: 2019-09-09 Last modified: 2020-09-06

Priority: 1

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Discussion:

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.

Either `readable_traits` should see through cv- and ref-qualifiers, or else the `readable` concept should strip top-level references when building the `iter_value_t` associated type (e.g., `iter_value_t<remove_reference_t<In>>`).

Suggest priority P1 because it effects the definition of a concept which cannot change after C++20.

[2019-10 Priority set to 1 after reflector discussion]

[2019-11 This should be resolved by P1878]

Previous resolution [SUPERSEDED]:

> This wording is relative to N4830.

> 1. Modify 25.3.4.2 [iterator.concept.readable], concept `readable` synopsis, as indicated:

>    >     template<class In>
>    >       concept readable =
>    >         requires {
>    >           typename iter_value_t<remove_reference_t<In>>;
>    >           typename iter_reference_t<In>;
>    >           typename iter_rvalue_reference_t<In>;
>    >         } &&
>    >         common_reference_with<iter_reference_t<In>&&, iter_value_t<remove_reference_t<In>>&> &&
>    >         common_reference_with<iter_reference_t<In>&&, iter_rvalue_reference_t<In>&&> &&
>    >         common_reference_with<iter_rvalue_reference_t<In>&&, const iter_value_t<remove_reference_t<In>>&>;

[2019-11; Resolved by the adoption of P1878 in Belfast]

Proposed resolution:

Resolved by P1878.