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Implement LWG-3785 ranges::to is over-constrained on the destination type being a range #3319

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merged 2 commits into from
Jan 12, 2023
Merged

Implement LWG-3785 ranges::to is over-constrained on the destination type being a range #3319

merged 2 commits into from
Jan 12, 2023

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frederick-vs-ja
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Fixes #3227.

I failed to figure out how to "convert a range of expected<T, E> to expected<vector<T>, E>" with ranges::to, so I just added some trivial test cases...

@frederick-vs-ja frederick-vs-ja requested a review from a team as a code owner January 1, 2023 15:50
@CaseyCarter CaseyCarter added LWG Library Working Group issue ranges C++20/23 ranges labels Jan 2, 2023
CaseyCarter
CaseyCarter approved these changes Jan 2, 2023
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stl/inc/ranges
@@ -7668,7 +7668,8 @@ namespace ranges {
// clang-format on

template <class _Rng, class _Container>
concept _Ref_converts = convertible_to<range_reference_t<_Rng>, range_value_t<_Container>>;
concept _Ref_converts =
(!input_range<_Container>) || convertible_to<range_reference_t<_Rng>, range_value_t<_Container>>;
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For other reviewers: these parentheses are needed only to avoid clang-format damage.

@hewillk
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hewillk commented Jan 8, 2023

I failed to figure out how to "convert a range of expected<T, E> to expected<vector<T>, E>" with ranges::to, so I just added some trivial test cases...

cc @brevzin

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brevzin commented Jan 8, 2023 •
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I failed to figure out how to "convert a range of expected<T, E> to expected<vector<T>, E>" with ranges::to, so I just added some trivial test cases...

cc @brevzin

Somebody would need to propose a new expected(from_range_t, R&&) constructor that does this, it's good that it doesn't work out of the box. The goal was simply to be able to support that kind of conversion for types that want to opt in to it.

And yeah, we should add that constructor (but... not in this PR of course).

@StephanTLavavej StephanTLavavej self-assigned this Jan 11, 2023
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I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

@StephanTLavavej StephanTLavavej merged commit a71aa52 into microsoft:main Jan 12, 2023
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Thanks for changing the STL to be more conformant and useful! 😹 🤪 🚀

@frederick-vs-ja frederick-vs-ja deleted the lwg-3785 branch January 12, 2023 01:21
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@strega-nil-ms strega-nil-ms strega-nil-ms approved these changes

@StephanTLavavej StephanTLavavej StephanTLavavej approved these changes

@CaseyCarter CaseyCarter CaseyCarter approved these changes

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LWG-3785 ranges::to is over-constrained on the destination type being a range
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@frederick-vs-ja @hewillk @brevzin @StephanTLavavej @CaseyCarter @strega-nil-ms