Add converting constructors, subset<U...>()

This commit is contained in:
Peter Dimov
2017-06-02 05:14:40 +03:00
parent 26c1f716ec
commit f4f949fc2f
3 changed files with 111 additions and 2 deletions

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@ -376,9 +376,10 @@ template<class T1, class... T> struct overload<T1, T...>: overload<T...>
#if BOOST_WORKAROUND( BOOST_MSVC, <= 1910 )
template<class U, class... T> struct resolve_overload_type_impl
template<class U, class... T> using resolve_overload_type_ = decltype( overload<T...>()(std::declval<U>()) );
template<class U, class... T> struct resolve_overload_type_impl: mp_defer< resolve_overload_type_, U, T... >
{
using type = decltype( overload<T...>()(std::declval<U>()) );
};
template<class U, class... T> using resolve_overload_type = typename resolve_overload_type_impl<U, T...>::type::type;
@ -991,6 +992,104 @@ public:
}
using variant_base::_get_impl;
// converting constructors (extension)
template<class... U,
class E2 = mp_if<mp_all<std::is_copy_constructible<U>..., mp_contains<mp_list<T...>, U>...>, void> >
variant( variant<U...> const& r )
noexcept( mp_all<std::is_nothrow_copy_constructible<U>...>::value )
{
mp_for_index<sizeof...(U)>( r.index(), [&]( auto I ){
using J = mp_find<mp_list<T...>, mp_at_c<mp_list<U...>, I>>;
::new( static_cast<variant_base*>(this) ) variant_base( J{}, r._get_impl( I ) );
});
}
template<class... U,
class E2 = mp_if<mp_all<std::is_move_constructible<U>..., mp_contains<mp_list<T...>, U>...>, void> >
variant( variant<U...> && r )
noexcept( mp_all<std::is_nothrow_move_constructible<U>...>::value )
{
mp_for_index<sizeof...(U)>( r.index(), [&]( auto I ){
using J = mp_find<mp_list<T...>, mp_at_c<mp_list<U...>, I>>;
::new( static_cast<variant_base*>(this) ) variant_base( J{}, std::move( r._get_impl( I ) ) );
});
}
// subset (extension)
private:
template<class... U, class V, std::size_t J, class E = std::enable_if_t<J != sizeof...(U)>> static variant<U...> _subset_impl( mp_size_t<J>, V && v )
{
return variant<U...>( in_place_index<J>, std::forward<V>(v) );
}
template<class... U, class V> static variant<U...> _subset_impl( mp_size_t<sizeof...(U)>, V && /*v*/ )
{
throw bad_variant_access();
}
public:
template<class... U,
class E2 = mp_if<mp_all<std::is_copy_constructible<U>..., mp_contains<mp_list<T...>, U>...>, void> >
constexpr variant<U...> subset() &
{
return mp_for_index<sizeof...(T)>( index(), [&]( auto I ){
using J = mp_find<mp_list<U...>, mp_at_c<mp_list<T...>, I>>;
return _subset_impl<U...>( J{}, get<I>( *this ) );
});
}
template<class... U,
class E2 = mp_if<mp_all<std::is_copy_constructible<U>..., mp_contains<mp_list<T...>, U>...>, void> >
constexpr variant<U...> subset() const&
{
return mp_for_index<sizeof...(T)>( index(), [&]( auto I ){
using J = mp_find<mp_list<U...>, mp_at_c<mp_list<T...>, I>>;
return _subset_impl<U...>( J{}, get<I>( *this ) );
});
}
template<class... U,
class E2 = mp_if<mp_all<std::is_copy_constructible<U>..., mp_contains<mp_list<T...>, U>...>, void> >
constexpr variant<U...> subset() &&
{
return mp_for_index<sizeof...(T)>( index(), [&]( auto I ){
using J = mp_find<mp_list<U...>, mp_at_c<mp_list<T...>, I>>;
return _subset_impl<U...>( J{}, get<I>( std::move(*this) ) );
});
}
template<class... U,
class E2 = mp_if<mp_all<std::is_copy_constructible<U>..., mp_contains<mp_list<T...>, U>...>, void> >
constexpr variant<U...> subset() const&&
{
return mp_for_index<sizeof...(T)>( index(), [&]( auto I ){
using J = mp_find<mp_list<U...>, mp_at_c<mp_list<T...>, I>>;
return _subset_impl<U...>( J{}, get<I>( std::move(*this) ) );
});
}
};
// relational operators

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@ -121,7 +121,12 @@ int main()
BOOST_TEST_TRAIT_FALSE((std::is_nothrow_copy_constructible<variant<X1, X2, int, int>>));
BOOST_TEST_TRAIT_TRUE((std::is_copy_constructible<variant<X1, X2>>));
#if !BOOST_WORKAROUND( BOOST_MSVC, <= 1910 )
BOOST_TEST_TRAIT_FALSE((std::is_copy_constructible<variant<int, float, Y>>));
#endif
}
return boost::report_errors();

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@ -122,7 +122,12 @@ int main()
BOOST_TEST_TRAIT_FALSE((std::is_nothrow_move_constructible<variant<X1, X2, int, int>>));
BOOST_TEST_TRAIT_TRUE((std::is_move_constructible<variant<X1, X2>>));
#if !BOOST_WORKAROUND( BOOST_MSVC, <= 1910 )
BOOST_TEST_TRAIT_FALSE((std::is_move_constructible<variant<int, float, Y>>));
#endif
}
return boost::report_errors();