Implement LWG-3843 std::expected<T,E>::value() & assumes E is copy constructible
#3737
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Also speculatively generalize the resolution to `expected<void, E>`.
StephanTLavavej
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May 28, 2023
StephanTLavavej
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May 29, 2023
strega-nil-ms
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Jun 8, 2023
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I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed. |
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Thanks for improving our conformance to the latest Working Paper as expected! 😹 🎉 🚀 |
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Per LWG-3843,
std::expected<int, std::unique_ptr<int>>{}.value()needs to be rejected. But currently MSVC and Clang incorrectly accept it (DevCom-1638273 and LLVM-53224).We also need to ensure that the
value() &overload also treats_Erras a const lvalue on copy.The mandating is missing in the standard wording in [expected.void.obs] currently, which is likely another LWG issue. I've mailed LWG chair for this.
Edit: the issue is now LWG-3940.