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ranges::distance fails to emulate the Standard's two overload presentation #2987

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Merged
Stephan T. Lavavej (StephanTLavavej) merged 5 commits into from
Aug 27, 2022
Merged

ranges::distance fails to emulate the Standard's two overload presentation #2987

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3d3e8a8
`ranges::distance` needs to better emulate the two overload presentat…
CaseyCarter Aug 3, 2022
dc5368a
Split the implementation per Nicole's request
CaseyCarter Aug 3, 2022
3a4bdc4
Merge remote-tracking branch 'upstream/main' into CaseyCarter/distanc…
strega-nil Aug 17, 2022
9213ec0
fix tests
strega-nil Aug 22, 2022
56e4509
Update comments.
StephanTLavavej Aug 26, 2022
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30 changes: 13 additions & 17 deletions stl/inc/xutility
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Original file line number Diff line number Diff line change
Expand Up @@ -2576,16 +2576,19 @@ namespace ranges {
public:
using _Not_quite_object::_Not_quite_object;

template <class _It, sentinel_for<decay_t<_It>> _Se>
_NODISCARD constexpr iter_difference_t<decay_t<_It>> operator()(_It&& _Raw_first, _Se _Last) const
noexcept(_Nothrow_dist<_It, _Se>) /* strengthened */ {
if constexpr (sized_sentinel_for<_Se, decay_t<_It>>) {
return _Last - static_cast<const decay_t<_It>&>(_Raw_first); // Per LWG-3664
} else {
auto _First = _STD forward<_It>(_Raw_first);
_Adl_verify_range(_First, _Last);
return _Distance_unchecked(_Get_unwrapped(_STD move(_First)), _Get_unwrapped(_STD move(_Last)));
}
template <class _It, sentinel_for<_It> _Se>
requires(!sized_sentinel_for<_Se, _It>)
_NODISCARD constexpr iter_difference_t<_It> operator()(_It _First, _Se _Last) const
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noexcept(noexcept(_Distance_unchecked(_Get_unwrapped(_STD move(_First)),
_Get_unwrapped(_STD move(_Last))))) /* strengthened */ { // Per LWG-3664
_Adl_verify_range(_First, _Last);
return _Distance_unchecked(_Get_unwrapped(_STD move(_First)), _Get_unwrapped(_STD move(_Last)));
}

template <class _It, sized_sentinel_for<decay_t<_It>> _Se>
_NODISCARD constexpr iter_difference_t<decay_t<_It>> operator()(_It&& _First, const _Se _Last) const
noexcept(noexcept(_Last - static_cast<const decay_t<_It>&>(_First))) /* strengthened */ { // Per LWG-3664
return _Last - static_cast<const decay_t<_It>&>(_First);
}

template <range _Rng>
Expand All @@ -2599,13 +2602,6 @@ namespace ranges {
}

private:
template <class _It, class _Se>
static constexpr bool _Nothrow_dist = false;

template <class _It, sized_sentinel_for<decay_t<_It>> _Se>
static constexpr bool _Nothrow_dist<_It, _Se> = noexcept(
_STD declval<_Se&>() - _STD declval<const decay_t<_It>&>());

template <class _It, class _Se>
_NODISCARD static constexpr iter_difference_t<_It> _Distance_unchecked(_It _First, const _Se _Last) noexcept(
noexcept(++_First != _Last)) {
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2 changes: 1 addition & 1 deletion tests/std/tests/P0896R4_ranges_iterator_machinery/test.cpp
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Expand Up @@ -2959,7 +2959,7 @@ namespace iter_ops {
trace t{};
I first{t};
same_as<iter_difference_t<I>> auto const result = distance(move(first), default_sentinel);
STATIC_ASSERT(!noexcept(distance(move(first), default_sentinel))); // No conditional noexcept
STATIC_ASSERT(noexcept(distance(move(first), default_sentinel)));
assert(result == sentinel_position);
assert((t == trace{.compares_ = sentinel_position + 1, .increments_ = sentinel_position}));
}
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