Implement LWG-3836 std::expected<bool, E1> conversion constructor expected(const expected<U, G>&) should take precedence over expected(U&&) with operator bool
#3587
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| @@ -239,19 +239,23 @@ public: | |||
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| template <class _Ty2> | |||
| using _AllowDirectConversion = bool_constant<conjunction_v<negation<is_same<_Remove_cvref_t<_Ty2>, optional>>, | |||
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Pre-existing, but why is this doing a bool_constant<conjunction_v rather than just conjunction; no change requested.
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I think there's some attempt here to improve throughput by "smashing" a complicated type to either true_type or false_type but looking at this again, I am unsure whether we are actually achieving anything here. In cases below (e.g. _AllowUnwrappingAssignment) we are introducing a new struct instead of simply a using, and there appears to be no short-circuit benefit to doing so. I'll record a todo on my list, but I would prefer to avoid touching this existing code in <optional> until Casey returns as there is no urgent need.
| std::expected<bool, DerivedError> e1(false); | ||
| std::expected<bool, BaseError> e2(e1); |
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No change requested: This test is already using namespace std;. Not worth resetting testing as this test has already accumulated ~20 occurrences; I'll clean this up later, no reason to pollute this PR.
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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 implementing one of the most verbosely-titled LWG issues ever! 😹 ✅ 🎉 |
Fixes #3433.