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value constructor is sfinae-friendly

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This commit is contained in:
Andrzej Krzemienski
2016-02-19 18:41:42 +01:00
parent 5ffa3fd2f6
commit f6e09fbf9c
6 changed files with 73 additions and 7 deletions
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35
include/boost/optional/optional.hpp
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@ -37,6 +37,7 @@
#include <boost/type_traits/remove_reference.hpp>
#include <boost/type_traits/decay.hpp>
#include <boost/type_traits/is_base_of.hpp>
#include <boost/type_traits/is_constructible.hpp>
#include <boost/type_traits/is_lvalue_reference.hpp>
#include <boost/type_traits/is_nothrow_move_assignable.hpp>
#include <boost/type_traits/is_nothrow_move_constructible.hpp>
@ -565,17 +566,39 @@ class optional_base : public optional_tag
storage_type m_storage ;
} ;
// definition of metafunciton is_optional_val_init_candidate
template <typename U>
struct is_optional_related
: boost::conditional<boost::is_base_of<optional_detail::optional_tag, BOOST_DEDUCED_TYPENAME boost::decay<U>::type>::value
|| boost::is_same<BOOST_DEDUCED_TYPENAME boost::decay<U>::type, none_t>::value,
: boost::conditional< boost::is_base_of<optional_detail::optional_tag, BOOST_DEDUCED_TYPENAME boost::decay<U>::type>::value
|| boost::is_same<BOOST_DEDUCED_TYPENAME boost::decay<U>::type, none_t>::value,
boost::true_type, boost::false_type>::type
{};
template <typename, typename U>
#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) && !defined(BOOST_NO_CXX11_DECLTYPE) && !BOOST_WORKAROUND(BOOST_MSVC, < 1800) && !BOOST_WORKAROUND(BOOST_GCC_VERSION, < 40500)
// this condition is a copy paste from is_constructible.hpp
template <typename T, typename U>
struct is_convertible_to_T_or_factory
: boost::conditional< boost::is_base_of<boost::in_place_factory_base, BOOST_DEDUCED_TYPENAME boost::decay<U>::type>::value
|| boost::is_base_of<boost::typed_in_place_factory_base, BOOST_DEDUCED_TYPENAME boost::decay<U>::type>::value
|| boost::is_constructible<T, U&&>::value
, boost::true_type, boost::false_type>::type
{};
#else
#define BOOST_OPTIONAL_DETAIL_NO_IS_CONSTRUCTIBLE_TRAIT
template <typename, typename>
struct is_convertible_to_T_or_factory : boost::true_type
{};
#endif // is_convertible condition
template <typename T, typename U>
struct is_optional_val_init_candidate
: boost::conditional<!is_optional_related<U>::value, boost::true_type, boost::false_type>::type
: boost::conditional< !is_optional_related<U>::value && is_convertible_to_T_or_factory<T, U>::value
, boost::true_type, boost::false_type>::type
{};
} // namespace optional_detail