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3375. decay in viewable_range should be remove_cvref

Section: 25.4.6 [range.refinements] Status: C++20 Submitter: Casey Carter Opened: 2020-01-14 Last modified: 2021-02-25

Priority: 0

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Discussion:

The viewable_range concept is defined in 25.4.6 [range.refinements] as:

template<class T>
  concept viewable_range =
    range<T> && (safe_range<T> || view<decay_t<T>>);

Since neither pointer types, array types, nor function types model view, view<decay_t<T>> here could simplified to view<remove_cvref_t<T>>. The use of decay_t is an artifact of the Ranges TS being based on C++14 which didn't have remove_cvref_t. [Note that the proposed change is not purely editorial since the difference is observable to subsumption.]

[2020-02-01 Status set to Tentatively Ready after five positive votes on the reflector.]

Previous resolution [SUPERSEDED]:

This wording is relative to N4842.

1. Modify 25.4.6 [range.refinements] as indicated:

   -4- The viewable_range concept specifies the requirements of a range type that can be converted to a view safely.

   template<class T>
     concept viewable_range =
       range<T> && (safe_range<T> || view<decay_tremove_cvref<T>>);
   

[2020-02-06 Casey provides a corrected P/R]

... in response to Jonathan's observation that remove_cvref<T> is both the wrong type and not what the discussion argues for.

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

Proposed resolution:

This wording is relative to N4849.

1. Modify 25.4.6 [range.refinements] as indicated:

   -4- The viewable_range concept specifies the requirements of a range type that can be converted to a view safely.

   template<class T>
     concept viewable_range =
       range<T> && (safe_range<T> || view<decay_tremove_cvref_t<T>>);