<algorithm>: Fix bogus pointer arithmetic with integer-class
#5091
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| auto vw = views::iota(I{}, static_cast<I>(ranges::size(a))) | ||
| | views::transform([&a](I i) -> auto& { return a[static_cast<size_t>(i)]; }); | ||
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| static_assert(three_way_comparable<ranges::iterator_t<ranges::iota_view<I>>>); // TRANSITION, /permissive |
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This is really weird. It seems that MSVC doesn't evaluate concept specializations as quickly as required in permissive modes.
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From the last bit of the error log:
D:\build\out\inc\__msvc_ranges_to.hpp(865): note: while evaluating concept 'three_way_comparable<std::ranges::_Ioterator<signed char>,std::partial_ordering>'
D:\build\out\inc\__msvc_ranges_to.hpp(865): error C2131: expression did not evaluate to a constant
D:\build\out\inc\__msvc_ranges_to.hpp(865): note: failure was caused by a read of an uninitialized symbol
D:\build\out\inc\__msvc_ranges_to.hpp(865): note: see usage of 'std::three_way_comparable<std::ranges::_Ioterator<_Wi>,std::partial_ordering>'
"C2131 while evaluating meow ... see usage of meow" generally suggests constraint recursion, which is not that unusual in permissive mode. The fact the overload resolution sees "extra" friend overloads that ought to be hidden can easily trigger constraint recursion.
| auto vw = views::iota(I{}, static_cast<I>(ranges::size(a))) | ||
| | views::transform([&a](I i) -> auto& { return a[static_cast<size_t>(i)]; }); | ||
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| static_assert(three_way_comparable<ranges::iterator_t<ranges::iota_view<I>>>); // TRANSITION, /permissive |
There was a problem hiding this comment.
From the last bit of the error log:
D:\build\out\inc\__msvc_ranges_to.hpp(865): note: while evaluating concept 'three_way_comparable<std::ranges::_Ioterator<signed char>,std::partial_ordering>'
D:\build\out\inc\__msvc_ranges_to.hpp(865): error C2131: expression did not evaluate to a constant
D:\build\out\inc\__msvc_ranges_to.hpp(865): note: failure was caused by a read of an uninitialized symbol
D:\build\out\inc\__msvc_ranges_to.hpp(865): note: see usage of 'std::three_way_comparable<std::ranges::_Ioterator<_Wi>,std::partial_ordering>'
"C2131 while evaluating meow ... see usage of meow" generally suggests constraint recursion, which is not that unusual in permissive mode. The fact the overload resolution sees "extra" friend overloads that ought to be hidden can easily trigger constraint recursion.
By using
ptrdiff_twhen the related value is guaranteed to be small enough and/or used in pointer arithmetic. Fixes #2885.