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[libc++][ranges] Fix ranges::to with ADL-only begin/end #119161

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[libc++][ranges] Fix ranges::to with ADL-only begin/end #119161

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1728e0f
[libc++][ranges] Fix `ranges::to` with ADL-only `begin`/`end`
frederick-vs-ja Dec 9, 2024
ed3a7f7
Merge branch 'main' into lwg-4016-regression
frederick-vs-ja Mar 2, 2025
ea3a23f
Switch to use `ranges::for_each`
frederick-vs-ja Mar 2, 2025
883ca4f
Workaround for lacking implementation of P0588R1
frederick-vs-ja Mar 2, 2025
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7 changes: 5 additions & 2 deletions libcxx/include/__ranges/to.h
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Original file line number Diff line number Diff line change
Expand Up @@ -109,8 +109,11 @@ template <class _Container, input_range _Range, class... _Args>
__result.reserve(static_cast<range_size_t<_Container>>(ranges::size(__range)));
}

for (auto&& __ref : __range) {
using _Ref = decltype(__ref);
auto __iter = ranges::begin(__range);
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@ldionne ldionne Jan 20, 2025

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I would suggest we use ranges::for_each instead, that seems cleaner and I don't think saving an include dependency is worth the added code complexity.

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@philnik777 philnik777 Jan 20, 2025

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I also wonder whether this would improve interactions with deque iterators.

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@frederick-vs-ja frederick-vs-ja Mar 2, 2025

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Switched to use ranges::for_each. I wonder whether range-for on ref_view{__range} suffices.

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@frederick-vs-ja frederick-vs-ja Mar 2, 2025

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This is somehow bad, as encountered in #113103 (comment).

auto __sent = ranges::end(__range);
for (; __iter != __sent; ++__iter) {
auto&& __ref = *__iter;
using _Ref = decltype(__ref);
if constexpr (requires { __result.emplace_back(std::declval<_Ref>()); }) {
__result.emplace_back(std::forward<_Ref>(__ref));
} else if constexpr (requires { __result.push_back(std::declval<_Ref>()); }) {
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19 changes: 19 additions & 0 deletions libcxx/test/std/ranges/range.utility/range.utility.conv/to.pass.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -550,11 +550,30 @@ constexpr void test_recursive() {
assert(std::ranges::to<C4>(in_owning_view) == result);
}

struct adl_only_range {
static constexpr int numbers[2]{42, 1729};

void begin() const = delete;
void end() const = delete;

friend constexpr const int* begin(const adl_only_range&) { return std::ranges::begin(numbers); }
friend constexpr const int* end(const adl_only_range&) { return std::ranges::end(numbers); }
};

constexpr void test_lwg4016_regression() {
using Cont = Container<int, CtrChoice::DefaultCtrAndInsert, InserterChoice::PushBack, true>;

std::ranges::contiguous_range auto r = adl_only_range{};
auto v = r | std::ranges::to<Cont>();
assert(std::ranges::equal(v, adl_only_range::numbers));
}

constexpr bool test() {
test_constraints();
test_ctr_choice_order();
test_lwg_3785();
test_recursive();
test_lwg4016_regression();

return true;
}
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