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<expected>: Workaround for DevCom-10655311 "Class derived from std::expected can't be constructed with bool value type" #4664

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May 21, 2024
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<expected>: Workaround for DevCom-10655311 "Class derived from std::expected can't be constructed with bool value type" #4664

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11 changes: 9 additions & 2 deletions stl/inc/expected
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Original file line number Diff line number Diff line change
Expand Up @@ -306,11 +306,18 @@ public:
template <class _Uty = _Ty>
requires (!is_same_v<remove_cvref_t<_Uty>, in_place_t> && !is_same_v<remove_cvref_t<_Uty>, expected>
&& !_Is_specialization_v<remove_cvref_t<_Uty>, unexpected>
&& (!is_same_v<remove_cv_t<_Ty>, bool> || !_Is_specialization_v<remove_cvref_t<_Uty>, expected>)
&& (!is_same_v<remove_cv_t<_Ty>, bool>
#if defined(__clang__) || defined(__EDG__) // TRANSITION, DevCom-10655311
|| !_Is_specialization_v<remove_cvref_t<_Uty>, expected>
#else // ^^^ no workaround / workaround vvv
|| !_Is_specialization_v<remove_cvref_t<_Uty>, _STD expected>
#endif // ^^^ workaround ^^^
)
&& is_constructible_v<_Ty, _Uty>)
constexpr explicit(!is_convertible_v<_Uty, _Ty>)
expected(_Uty&& _Other) noexcept(is_nothrow_constructible_v<_Ty, _Uty>) // strengthened
: _Value(_STD forward<_Uty>(_Other)), _Has_value(true) {}
: _Value(_STD forward<_Uty>(_Other)), _Has_value(true) {
}

template <class _UErr>
requires is_constructible_v<_Err, const _UErr&>
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25 changes: 25 additions & 0 deletions tests/std/tests/P0323R12_expected/test.cpp
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Expand Up @@ -2317,6 +2317,30 @@ void test_lwg_3843() {
static_assert(copyable<expected<any, int>>);
static_assert(copyable<expected<void, any>>);

// Test workaround for DevCom-10655311: Class derived from std::expected can't be constructed with bool value type
template <class T, class E>
class DerivedFromExpected : private expected<T, E> {
public:
using expected<T, E>::expected;
using expected<T, E>::value;
};

static_assert(is_constructible_v<DerivedFromExpected<bool, int>, bool>);
static_assert(is_constructible_v<DerivedFromExpected<bool, int>, const bool&>);

constexpr bool test_inherited_constructors() {
DerivedFromExpected<bool, int> wrapped_false_val(false);
assert(!wrapped_false_val.value());

constexpr bool true_val = true;
DerivedFromExpected<bool, int> wrapped_true_val(true_val);
assert(wrapped_true_val.value());

return true;
}

static_assert(test_inherited_constructors());

int main() {
test_unexpected::test_all();
static_assert(test_unexpected::test_all());
Expand All @@ -2333,4 +2357,5 @@ int main() {

test_reinit_regression();
test_lwg_3843();
test_inherited_constructors();
}