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ranges::minmax_elementSection: 26.4[algorithm.syn]Status:C++20Submitter: Casey CarterOpened: 2018-12-21Last modified: 2021-02-25
Priority:0
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Discussion:
The overloads ofstd::ranges::minmax_element are specified to returnstd::ranges::minmax_result, which is inconsistent with the intendeddesign. When an algorithmfoo returns an aggregate of multiple results,the return type should be namedfoo_result.The spec should introduce an aliasminmax_element_result forminmax_result and use that alias as the return type of thestd::ranges::minmax_element overloads.
[2019-01-11 Status to Tentatively Ready after five positive votes on the reflector.]
During that reflector discussion several contributers questioned the choice of alias templates to denotealgorithm result types or particular aspects of it. Since this approach had been approved by LEWG before, it was suggested to those opponents to instead write a paper, because changing this as part of this issue would be a design change that would require a more global fixing approach.
Proposed resolution:
This wording is relative toN4791.
Change 26.4[algorithm.syn] as indicated, and adjust thedeclarations ofstd::ranges::minmax_elementin 26.8.9[alg.min.max] to agree:
[…]template<class ExecutionPolicy, class ForwardIterator, class Compare> pair<ForwardIterator, ForwardIterator> minmax_element(ExecutionPolicy&& exec, // see 26.3.5[algorithms.parallel.overloads] ForwardIterator first, ForwardIterator last, Compare comp);namespace ranges {template<class I>using minmax_element_result = minmax_result<I>; template<ForwardIterator I, Sentinel<I> S, class Proj = identity, IndirectStrictWeakOrder<projected<I, Proj>> Comp = ranges::less<>> constexpr minmax_element_result<I> minmax_element(I first, S last, Comp comp = {}, Proj proj = {}); template<ForwardRange R, class Proj = identity, IndirectStrictWeakOrder<projected<iterator_t<R>, Proj>> Comp = ranges::less<>> constexpr minmax_element_result<safe_iterator_t<R>> minmax_element(R&& r, Comp comp = {}, Proj proj = {});}// 26.8.10[alg.clamp], bounded value[…]