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Implement LWG-3564: transform_view::iterator<true>::value_type and iterator_category should use const F& #2961

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merged 11 commits into from
Aug 5, 2022
Merged

Implement LWG-3564: transform_view::iterator<true>::value_type and iterator_category should use const F& #2961

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b5cdb12
Test coverage for LWG-3564
frederick-vs-ja Jul 27, 2022
3fd73dd
Implement LWG-3564
frederick-vs-ja Jul 27, 2022
7269026
Rewrite the test cases
frederick-vs-ja Jul 28, 2022
f0632af
Merge branch 'microsoft:main' into lwg-3564
frederick-vs-ja Jul 28, 2022
66c2d3f
Clang-format: unbreak line
frederick-vs-ja Jul 28, 2022
ac62cc5
Fix serious copy-pasta
frederick-vs-ja Jul 28, 2022
8a595d3
Fix serious copy-pasta, again
frederick-vs-ja Jul 28, 2022
33c7f39
Reimplement _Category_base to support transform_view<const X, F>
frederick-vs-ja Jul 28, 2022
aa32b81
Revert some changes
frederick-vs-ja Jul 28, 2022
a1fbdeb
Addresss @miscco's review comments
frederick-vs-ja Jul 29, 2022
ab6d554
Fix a serious missing change
frederick-vs-ja Jul 29, 2022
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14 changes: 7 additions & 7 deletions stl/inc/ranges
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Original file line number Diff line number Diff line change
Expand Up @@ -1908,11 +1908,11 @@ namespace ranges {

template <forward_range _Base>
struct _Category_base<_Base> {
using iterator_category =
conditional_t<is_lvalue_reference_v<invoke_result_t<_Fn&, range_reference_t<_Base>>>,
conditional_t<derived_from<_Iter_cat_t<iterator_t<_Base>>, contiguous_iterator_tag>,
random_access_iterator_tag, _Iter_cat_t<iterator_t<_Base>>>,
input_iterator_tag>;
using iterator_category = conditional_t<
is_lvalue_reference_v<invoke_result_t<_Maybe_const<is_const_v<_Base>, _Fn>&, range_reference_t<_Base>>>,
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conditional_t<derived_from<_Iter_cat_t<iterator_t<_Base>>, contiguous_iterator_tag>,
random_access_iterator_tag, _Iter_cat_t<iterator_t<_Base>>>,
input_iterator_tag>;
};

template <bool _Const>
Expand Down Expand Up @@ -1946,8 +1946,8 @@ namespace ranges {
using iterator_concept = conditional_t<random_access_range<_Base>, random_access_iterator_tag,
conditional_t<bidirectional_range<_Base>, bidirectional_iterator_tag,
conditional_t<forward_range<_Base>, forward_iterator_tag, input_iterator_tag>>>;
using value_type = remove_cvref_t<invoke_result_t<_Fn&, range_reference_t<_Base>>>;
using difference_type = range_difference_t<_Base>;
using value_type = remove_cvref_t<invoke_result_t<_Maybe_const<_Const, _Fn>&, range_reference_t<_Base>>>;
using difference_type = range_difference_t<_Base>;

// clang-format off
_Iterator() requires default_initializable<iterator_t<_Base>> = default;
Expand Down
47 changes: 47 additions & 0 deletions tests/std/tests/P0896R4_views_transform/test.cpp
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Expand Up @@ -321,6 +321,50 @@ constexpr bool test_one(Rng&& rng, Expected&& expected) {
return true;
}

// Test a function object whose const and non-const versions behave differently
struct difference_teller {
constexpr auto& operator()(auto&& x) noexcept {
auto& ref = x;
return ref;
}

constexpr auto operator()(auto&& x) const noexcept {
return type_identity<decltype(x)>{};
}
};

template <ranges::input_range Rng>
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constexpr void test_difference_on_const_functor(Rng&& rng) {
using ranges::transform_view, ranges::input_range, ranges::forward_range, ranges::bidirectional_range,
ranges::random_access_range, ranges::iterator_t, ranges::range_reference_t, ranges::range_value_t;

using V = views::all_t<Rng>;
using TV = transform_view<V, difference_teller>;

auto r = forward<Rng>(rng) | views::transform(difference_teller{});
STATIC_ASSERT(is_same_v<decltype(r), TV>);

STATIC_ASSERT(is_lvalue_reference_v<range_reference_t<TV>>);
if constexpr (input_range<const TV>) {
STATIC_ASSERT(is_object_v<range_reference_t<const TV>>);
STATIC_ASSERT(!is_same_v<range_value_t<TV>, range_value_t<const TV>>);
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}

if constexpr (forward_range<V>) {
using It = iterator_t<V>;
using TVIt = iterator_t<TV>;
using VItCat = typename iterator_traits<It>::iterator_category;
using TVItCat = typename iterator_traits<TVIt>::iterator_category;
STATIC_ASSERT(
is_same_v<TVItCat, VItCat> //
|| (is_same_v<TVItCat, random_access_iterator_tag> && is_same_v<VItCat, contiguous_iterator_tag>) );
}

if constexpr (forward_range<const V>) {
STATIC_ASSERT(is_same_v<typename iterator_traits<iterator_t<const TV>>::iterator_category, input_iterator_tag>);
}
}

static constexpr int some_ints[] = {0, 1, 2, 3, 4, 5, 6, 7};
static constexpr int transformed_ints[] = {8, 9, 10, 11, 12, 13, 14, 15};

Expand All @@ -329,6 +373,9 @@ struct instantiator {
static constexpr void call() {
R r{some_ints};
test_one(r, transformed_ints);

R r2{some_ints};
test_difference_on_const_functor(r2);
}
};

Expand Down