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added is_reference_wrapper<>, unwrap_reference<>

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[SVN r12470]
This commit is contained in:
Dave Abrahams 2002-01-23 21:19:14 +00:00
parent c7c09696db
commit f3f697bbc8
1 changed files with 91 additions and 10 deletions
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81
include/boost/ref.hpp
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@ -25,6 +25,7 @@ namespace boost
template<class T> class reference_wrapper
{
public:
typedef T type;
explicit reference_wrapper(T & t): t_(t) {}
@ -57,6 +58,86 @@ template<class T> inline reference_wrapper<T const> BOOST_REF_CONST cref(T const
# undef BOOST_REF_CONST
# ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
template<typename T>
class is_reference_wrapper
{
public:
BOOST_STATIC_CONSTANT(bool, value = false);
};
template<typename T>
class is_reference_wrapper<reference_wrapper<T> >
{
public:
BOOST_STATIC_CONSTANT(bool, value = true);
};
template<typename T>
class unwrap_reference
{
public:
typedef T type;
};
template<typename T>
class unwrap_reference<reference_wrapper<T> >
{
public:
typedef T type;
};
# else // no partial specialization
namespace detail
{
typedef char (&yes_reference_wrapper_t)[1];
typedef char (&no_reference_wrapper_t)[2];
no_reference_wrapper_t is_reference_wrapper_test(...);
template<typename T>
yes_reference_wrapper_t is_reference_wrapper_test(reference_wrapper<T>*);
template<bool wrapped>
struct reference_unwrapper
{
template <class T>
struct apply
{
typedef T type;
};
};
template<>
struct reference_unwrapper<true>
{
template <class T>
struct apply
{
typedef typename T::type type;
};
};
}
template<typename T>
class is_reference_wrapper
{
public:
static T* t;
BOOST_STATIC_CONSTANT(
bool, value = (
sizeof(detail::is_reference_wrapper_test(t))
== sizeof(detail::yes_reference_wrapper_t)));
};
template <typename T>
class unwrap_reference
: public detail::reference_unwrapper<
is_reference_wrapper<T>::value
>::template apply<T>
{};
# endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
} // namespace boost
#endif // #ifndef BOOST_REF_HPP_INCLUDED