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Implement LWG-3420 #786

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May 5, 2020
Merged

Implement LWG-3420 #786

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1db6798
Implement LWG-3420
CaseyCarter May 4, 2020
f42fd6d
Update stl/inc/xutility
CaseyCarter May 4, 2020
b64aae2
Update tests/std/tests/P0896R4_ranges_iterator_machinery/test.cpp
CaseyCarter May 4, 2020
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12 changes: 7 additions & 5 deletions stl/inc/xutility
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Original file line number Diff line number Diff line change
Expand Up @@ -431,11 +431,13 @@ struct _Iter_traits_difference<false> {

// clang-format off
template <class _It>
concept _Cpp17_iterator = copyable<_It> && requires(_It __i) {
{ *__i } -> _Can_reference;
{ ++__i } -> same_as<_It&>;
{ *__i++ } -> _Can_reference;
};
concept _Cpp17_iterator = // per LWG-3420
requires(_It __i) {
{ *__i } -> _Can_reference;
{ ++__i } -> same_as<_It&>;
{ *__i++ } -> _Can_reference;
}
&& copyable<_It>;

template <class _It>
concept _Cpp17_input_iterator = _Cpp17_iterator<_It>
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14 changes: 14 additions & 0 deletions tests/std/tests/P0896R4_ranges_iterator_machinery/test.cpp
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Expand Up @@ -2986,6 +2986,20 @@ namespace reverse_iterator_test {
!std::sized_sentinel_for<reverse_iterator<simple_no_difference>, reverse_iterator<simple_no_difference>>);
} // namespace reverse_iterator_test

namespace lwg3420 {
// Validate that we can ask for the iterator_traits of a type with no operator* for which checking copyability
// results in constraint recursion.
struct X {
X() = default;
template <std::copyable T>
X(T const&);
};
STATIC_ASSERT(!has_member_iter_concept<std::iterator_traits<X>>);
STATIC_ASSERT(!has_member_iter_category<std::iterator_traits<X>>);
STATIC_ASSERT(!has_member_difference_type<std::iterator_traits<X>>);
STATIC_ASSERT(!has_member_value_type<std::iterator_traits<X>>);
} // namespace lwg3420

int main() {
iterator_cust_swap_test::test();
iter_ops::test();
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