Implement P0798R8 monadic operations for std::optional #2301
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tests/std/tests/P0798R8_monadic_operations_for_std_optional/test.cpp
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tests/std/tests/P0798R8_monadic_operations_for_std_optional/test.cpp
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| using _Uty = invoke_result_t<_Fn, _Ty&>; | ||
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| static_assert(_Is_specialization_v<remove_cvref_t<_Uty>, optional>, | ||
| "optional<T>::and_then(F) requires the return type of F to be a specialization of optional " |
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With the remove_cvref_t, this is more "requires the type of f(value()) (where f denotes the argument to and_then) to be a cv-qualified specialization of optional" but that's too precise to be clear to the people who actually need this message. Maybe "requires the argument to return a specialization of optional"?
No change required if you don't feel it's an improvement, but if you do please change all four places consistently.
| using _Uty = remove_cv_t<invoke_result_t<_Fn, _Ty&>>; | ||
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| static_assert(!_Is_any_of_v<_Uty, nullopt_t, in_place_t>, | ||
| "optional<T>::transform(F) requires the return type of F to be a type other than nullopt_t or in_place_t " |
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Technically "other than cv-nullopt_t or cv-in_place_t", but that's strictly worse. (Please don't change.)
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I decided to simply push a commit to correct a couple of syntax nits and verify preconditions of a test function. I'll move this to Ready to Merge, but feel free to address the pure suggestion comments I left if you like. |
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I'll add this to the PR mirror that I'm preparing now. If cleanup changes are desired, they can go into a followup PR. Please inform me if any further changes are pushed to this PR, or if I should exclude it from this batch for any reason. |
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Pushed a merge with |
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Thanks for implementing this C++23 feature! 😻 ✅ 🚀 |
Implements Monadic Operations for
std::optionalas specified in [optional.monadic].Fixes #2242
I applied(edit: removed after code review)_NODISCARDto all overloads, since they all return a value, though it's possible that someone wants to use them for control flow and ignore the return value.