std::add_pointer(3)

NAME
std::add_pointer - std::add_pointer

Synopsis
   Defined in header <type_traits>
   template< class T > (since C++11)
   struct add_pointer;
   If T is a referenceable type or (possibly cv-qualified) void, the member typedef
   type provided is typename std::remove_reference::type<T>*.
   Otherwise, the member typedef type provided is T.
   If the program adds specializations for std::add_pointer, the behavior is undefined.

Helper types
   template< class T > (since C++14)
   using add_pointer_t = typename add_pointer<T>::type;

Possible implementation
  namespace detail
  {
      template<class T>
      struct type_identity { using type = T; }; // or use std::type_identity (since C++20)
      template<class T>
      auto try_add_pointer(int)
        -> type_identity<typename std::remove_reference<T>::type*>; // usual case
      template<class T>
      auto try_add_pointer(...)
        -> type_identity<T>; // unusual case (cannot form std::remove_reference<T>::type*)
  } // namespace detail
  template<class T>
  struct add_pointer : decltype(detail::try_add_pointer<T>(0)) {};

Example
// Run this code
 #include <iostream>
 #include <type_traits>
 template<typename F, typename Class>
 void ptr_to_member_func_cvref_test(F Class::*)
 {
     // F is an “abominable function type”
     using FF = std::add_pointer_t<F>;
     static_assert(std::is_same_v<F, FF>, "FF should be precisely F");
 }
 struct S
 {
     void f_ref() & {}
     void f_const() const {}
 };
 int main()
 {
     int i = 123;
     int& ri = i;
     typedef std::add_pointer<decltype(i)>::type IntPtr;
     typedef std::add_pointer<decltype(ri)>::type IntPtr2;
     IntPtr pi = &i;
     std::cout << "i = " << i << '\n';
     std::cout << "*pi = " << *pi << '\n';
     static_assert(std::is_pointer_v<IntPtr>, "IntPtr should be a pointer");
     static_assert(std::is_same_v<IntPtr, int*>, "IntPtr should be a pointer to int");
     static_assert(std::is_same_v<IntPtr2, IntPtr>, "IntPtr2 should be equal to IntPtr");
     typedef std::remove_pointer<IntPtr>::type IntAgain;
     IntAgain j = i;
     std::cout << "j = " << j << '\n';
     static_assert(!std::is_pointer_v<IntAgain>, "IntAgain should not be a pointer");
     static_assert(std::is_same_v<IntAgain, int>, "IntAgain should be equal to int");
     ptr_to_member_func_cvref_test(&S::f_ref);
     ptr_to_member_func_cvref_test(&S::f_const);
 }

Output:
 i = 123
 *pi = 123
 j = 123
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
   LWG 2101 C++11 the program was ill-formed if T is a the type produced is T in
                       function type with cv or ref this case

See also
   is_pointer checks if a type is a pointer type
   (C++11) (class template)
   remove_pointer removes a pointer from the given type
   (C++11) (class template)