20 Memory management library [mem]

20.2 Memory [memory]

20.2.3 Pointer traits [pointer.traits] Member types [pointer.traits.types]

The definitions in this subclause make use of the following exposition-only class template and concept: template<class T> struct ptr-traits-elem // exposition only { }; template<class T> requires requires { typename T::element_type; } struct ptr-traits-elem<T> { using type = typename T::element_type; }; template<template<class...> class SomePointer, class T, class... Args> requires (!requires { typename SomePointer<T, Args...>::element_type; }) struct ptr-traits-elem<SomePointer<T, Args...>> { using type = T; }; template<class Ptr> concept has-elem-type = // exposition only requires { typename ptr-traits-elem<Ptr>::type; }
If Ptr satisfies has-elem-type, a specialization pointer_traits<Ptr> generated from the pointer_traits primary template has the following members as well as those described in [pointer.traits.functions]; otherwise, such a specialization has no members by any of those names.
using pointer = see below;
Type: Ptr.
using element_type = see below;
Type: typename ptr-traits-elem<Ptr>​::​type.
using difference_type = see below;
Type: Ptr​::​difference_type if the qualified-id Ptr​::​difference_type is valid and denotes a type ([temp.deduct]); otherwise, ptrdiff_t.
template<class U> using rebind = see below;
Alias template: Ptr​::​rebind<U> if the qualified-id Ptr​::​rebind<U> is valid and denotes a type ([temp.deduct]); otherwise, SomePointer<U, Args> if Ptr is a class template instantiation of the form SomePointer<T, Args>, where Args is zero or more type arguments; otherwise, the instantiation of rebind is ill-formed.