The class template allocator_traits supplies a uniform interface to all allocator types. An allocator cannot be a non-class type, however, even if allocator_traits supplies the entire required interface. [ Note: Thus, it is always possible to create a derived class from an allocator. — end note ]
namespace std {
template <class Alloc> struct allocator_traits {
using allocator_type = Alloc;
using value_type = typename Alloc::value_type;
using pointer = see below;
using const_pointer = see below;
using void_pointer = see below;
using const_void_pointer = see below;
using difference_type = see below;
using size_type = see below;
using propagate_on_container_copy_assignment = see below;
using propagate_on_container_move_assignment = see below;
using propagate_on_container_swap = see below;
using is_always_equal = see below;
template <class T> using rebind_alloc = see below;
template <class T> using rebind_traits = allocator_traits<rebind_alloc<T>>;
static pointer allocate(Alloc& a, size_type n);
static pointer allocate(Alloc& a, size_type n, const_void_pointer hint);
static void deallocate(Alloc& a, pointer p, size_type n);
template <class T, class... Args>
static void construct(Alloc& a, T* p, Args&&... args);
template <class T>
static void destroy(Alloc& a, T* p);
static size_type max_size(const Alloc& a) noexcept;
static Alloc select_on_container_copy_construction(const Alloc& rhs);
};
}
Type: Alloc::pointer if the qualified-id Alloc::pointer is valid and denotes a type ([temp.deduct]); otherwise, value_type*.
using const_pointer = see below;
Type: Alloc::const_pointer if the qualified-id Alloc::const_pointer is valid and denotes a type ([temp.deduct]); otherwise, pointer_traits<pointer>::rebind<const value_type>.
using void_pointer = see below;
Type: Alloc::void_pointer if the qualified-id Alloc::void_pointer is valid and denotes a type ([temp.deduct]); otherwise, pointer_traits<pointer>::rebind<void>.
using const_void_pointer = see below;
Type: Alloc::const_void_pointer if the qualified-id Alloc::const_void_pointer is valid and denotes a type ([temp.deduct]); otherwise, pointer_traits<pointer>::rebind<const void>.
using difference_type = see below;
Type: Alloc::difference_type if the qualified-id Alloc::difference_type is valid and denotes a type ([temp.deduct]); otherwise, pointer_traits<pointer>::difference_type.
Type: Alloc::size_type if the qualified-id Alloc::size_type is valid and denotes a type ([temp.deduct]); otherwise, make_unsigned_t<difference_type>.
using propagate_on_container_copy_assignment = see below;
Type: Alloc::propagate_on_container_copy_assignment if the qualified-id Alloc::propagate_on_container_copy_assignment is valid and denotes a type ([temp.deduct]); otherwise false_type.
using propagate_on_container_move_assignment = see below;
Type: Alloc::propagate_on_container_move_assignment if the qualified-id Alloc::propagate_on_container_move_assignment is valid and denotes a type ([temp.deduct]); otherwise false_type.
using propagate_on_container_swap = see below;
Type: Alloc::propagate_on_container_swap if the qualified-id Alloc::propagate_on_container_swap is valid and denotes a type ([temp.deduct]); otherwise false_type.
using is_always_equal = see below;
Type: Alloc::is_always_equal if the qualified-id Alloc::is_always_equal is valid and denotes a type ([temp.deduct]); otherwise is_empty<Alloc>::type.
template <class T> using rebind_alloc = see below;
Alias template: Alloc::rebind<T>::other if the qualified-id Alloc::rebind<T>::other is valid and denotes a type ([temp.deduct]); otherwise, Alloc<T, Args> if Alloc is a class template instantiation of the form Alloc<U, Args>, where Args is zero or more type arguments; otherwise, the instantiation of rebind_alloc is ill-formed.
static pointer allocate(Alloc& a, size_type n);
Returns: a.allocate(n).
static pointer allocate(Alloc& a, size_type n, const_void_pointer hint);
Returns: a.allocate(n, hint) if that expression is well-formed; otherwise, a.allocate(n).
static void deallocate(Alloc& a, pointer p, size_type n);
Effects: Calls a.deallocate(p, n).
Throws: Nothing.
template <class T, class... Args>
static void construct(Alloc& a, T* p, Args&&... args);
Effects: Calls a.construct(p, std::forward<Args>(args)...) if that call is well-formed; otherwise, invokes ::new (static_cast<void*>(p)) T(std::forward<Args>(args)...).
template <class T>
static void destroy(Alloc& a, T* p);
Effects: Calls a.destroy(p) if that call is well-formed; otherwise, invokes p->~T().
static size_type max_size(const Alloc& a) noexcept;
Returns: a.max_size() if that expression is well-formed; otherwise, numeric_limits<size_type>::max()/sizeof(value_type).
static Alloc select_on_container_copy_construction(const Alloc& rhs);
Returns: rhs.select_on_container_copy_construction() if that expression is well-formed; otherwise, rhs.