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Section: 26.5.4 [range.subrange] Status: C++23 Submitter: Casey Carter Opened: 2020-02-20 Last modified: 2023-11-22
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Both LWG 3281 "Conversion from pair-like types to subrange is a silent semantic promotion" and LWG 3282 "subrange converting constructor should disallow derived to base conversions" removed subrange's hated implicit conversions from pair-like types. Notably, neither issue removed the two "iterator-sentinel-pair" deduction guides which target the removed constructors nor the exposition-only iterator-sentinel-pair concept itself, all of which are now useless.
[2020-03-11 Issue Prioritization]
Status set to Tentatively Ready after seven positive votes on the reflector.
[2020-11-09 Approved In November virtual meeting. Status changed: Tentatively Ready → WP.]
This wording is relative to N4849.
Modify 26.5.4 [range.subrange] as indicated:
[…] template<class T, class U, class V> concept pair-like-convertible-from = // exposition only !range<T> && pair-like<T> && constructible_from<T, U, V>;
template<class T> concept iterator-sentinel-pair = // exposition only !range<T> && pair-like<T> && sentinel_for<tuple_element_t<1, T>, tuple_element_t<0, T>>;[…] template<iterator-sentinel-pair P> subrange(P) -> subrange<tuple_element_t<0, P>, tuple_element_t<1, P>>; template<iterator-sentinel-pair P> subrange(P, make-unsigned-like-t(iter_difference_t<tuple_element_t<0, P>>)) -> subrange<uple_element_t<0, P>, tuple_element_t<1, P>, subrange_kind::sized>;[…]