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3351.ranges::enable_safe_range should not be constrained
Section: 25.2 [ranges.syn] Status: C++20 Submitter: Jonathan Wakely Opened: 2019-12-05 Last modified: 2021-02-25
Priority: 0
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Discussion:
Currently ranges::enable_safe_range is constrained with ranges::range, which not only forces the compiler to do unnecessary satisfaction checking when it's used, but also creates a tricky dependency cycle (ranges::range depends on ranges::begin which depends on ranges::enable_safe_range which depends on ranges::range).
ranges::safe_range concept, which already checks range<T> before using enable_safe_range<T> anyway. The constraint serves no purpose and should be removed.
[2019-12-12 Issue Prioritization]
Status to Tentatively Ready and priority to 0 after eight positive votes on the reflector.
Proposed resolution:
This wording is relative to N4842.
Modify 25.2 [ranges.syn] as indicated:
[Drafting note: The definition in 25.4.2 [range.range] p7 is already unconstrained, which contradicts the synopsis.]
[…] // 25.4.2 [range.range], ranges template<class T> concept range = see below; template<rangeclass T> inline constexpr bool enable_safe_range = false; template<class T> concept safe_range = see below; […]
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