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Enable implicit construction when the alternative is explicitly constructible from the argument. Fixes #103.

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Peter Dimov
2023-01-21 20:09:53 +02:00
parent 456b3c2dad
commit f0b27c5826
2 changed files with 10 additions and 4 deletions
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4
include/boost/system/result.hpp
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@ -122,7 +122,7 @@ public:
template<class A = T, typename std::enable_if< template<class A = T, typename std::enable_if<
std::is_convertible<A, T>::value && std::is_convertible<A, T>::value &&
!(detail::is_errc_t<A>::value && std::is_arithmetic<T>::value) && !(detail::is_errc_t<A>::value && std::is_arithmetic<T>::value) &&
!std::is_constructible<E, A>::value, int>::type = 0> !std::is_convertible<A, E>::value, int>::type = 0>
constexpr result( A&& a ) constexpr result( A&& a )
noexcept( std::is_nothrow_constructible<T, A>::value ) noexcept( std::is_nothrow_constructible<T, A>::value )
: v_( in_place_value, std::forward<A>(a) ) : v_( in_place_value, std::forward<A>(a) )
@ -132,7 +132,7 @@ public:
// implicit, error // implicit, error
template<class A = E, class = void, typename std::enable_if< template<class A = E, class = void, typename std::enable_if<
std::is_convertible<A, E>::value && std::is_convertible<A, E>::value &&
!std::is_constructible<T, A>::value, int>::type = 0> !std::is_convertible<A, T>::value, int>::type = 0>
constexpr result( A&& a ) constexpr result( A&& a )
noexcept( std::is_nothrow_constructible<E, A>::value ) noexcept( std::is_nothrow_constructible<E, A>::value )
: v_( in_place_error, std::forward<A>(a) ) : v_( in_place_error, std::forward<A>(a) )

10
test/result_error_construct.cpp
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@ -146,8 +146,14 @@ int main()
BOOST_TEST_TRAIT_TRUE((std::is_constructible<result<std::string, X>, int>)); BOOST_TEST_TRAIT_TRUE((std::is_constructible<result<std::string, X>, int>));
BOOST_TEST_TRAIT_FALSE((std::is_convertible<int, result<std::string, X>>)); BOOST_TEST_TRAIT_FALSE((std::is_convertible<int, result<std::string, X>>));
BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int, X>, int>)); // We'd like this to be false due to the ambiguity caused by X having
BOOST_TEST_TRAIT_FALSE((std::is_convertible<int, result<int, X>>)); // an explicit constructor taking an int, which should be viable in this
// context, but the implicit constructor is enabled, and there's no way to
// disallow it
//
// BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int, X>, int>));
BOOST_TEST_TRAIT_TRUE((std::is_convertible<int, result<int, X>>));
} }
{ {