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The header <boost/core/pointer_traits.hpp> provides the class template
boost::pointer_traits
to facilitate use of pointer-like
types. The C++11 standard library introduced std::pointer_traits
along with an allocator model which supported pointer-like types in addition
to plain raw pointers. This implementation also supports C++98, and adds
additional functionality for obtaining raw pointers from pointers.
The following function template obtains a raw pointer from a pointer and is well defined when the pointer aliases storage that has no object constructed in it.
template<class T> inline typename boost::pointer_traits<T>::element_type* to_raw_pointer(T v) noexcept { return boost::pointer_traits<T>::to_address(v); }
namespace boost { template<class T> struct pointer_traits { typedef T pointer; typedef see below element_type; typedef see below difference_type; template<class U> struct rebind_to { typedef see below type; }; template<class U> using rebind = typename rebind_to<U>::type; static pointer pointer_to(see below v); static element_type* to_address(pointer v) noexcept; }; template<class T> struct pointer_traits<T*> { typedef T* pointer; typedef T element_type; typedef std::ptrdiff_t difference_type; template<class U> struct rebind_to { typedef U* type; }; template<class U> using rebind = typename rebind_to<U>::type; static pointer pointer_to(see below v) noexcept; static element_type* to_address(pointer v) noexcept; }; }
typedef
see
below element_type;
T::element_type
if such a type
exists; otherwise U
if T
is a class
template instantiation of the form Pointer<U, Args>
, where Args
is zero or more type arguments; otherwise the specialization
is ill-formed.
typedef
see
below difference_type;
T::difference_type
if such a
type exists; otherwise std::ptrdiff_t
.
template<class U> struct
rebind_to {
typedef
see below
type;
};
type
is T::rebind<U>
if such a type exists; otherwise, Pointer<V, Args>
if T
is a class template instantiation of the form Pointer<T,
Args>
,
where Args
is zero or more type arguments; otherwise, the instantiation
of rebind_to
is ill-formed.
pointer_traits
static pointer
pointer_to(
see
below v);
If element_type
is a void type, the type of v
is unspecified; otherwise, it is element_type&
.
A pointer to v
obtained by calling T::pointer_to(v)
.
static element_type* to_address(pointer
v)
noexcept;
v
is not a
null pointer.
A pointer of type element_type*
that references the same location
as the argument.
pointer_traits<T*>
static pointer
pointer_to(
see
below v)
noexcept;
If element_type
is a void type, the type of v
is unspecified; otherwise, it is element_type&
.
The result of std::addressof(v)
.
static element_type* to_address(pointer
v)
noexcept;
The value of v
.
Glen Fernandes implemented pointer_traits
with reviews and guidance from Peter Dimov.