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 reference type, then provides the member typedef type which is a pointer
   to the referred type.
   Otherwise, if T names an object type, a function type that is not cv- or
   ref-qualified, or a (possibly cv-qualified) void type, provides the member typedef
   type which is the type T*.
   Otherwise (if T is a cv- or ref-qualified function type), provides the member
   typedef type which is the type T.
   The behavior of a program that adds specializations for add_pointer is undefined.

Member types
   Name Definition
   type pointer to T or to the type referenced by T

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*>;
   template <class T>
   auto try_add_pointer(...) -> type_identity<T>;
   } // 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<IntPtr>::value, "IntPtr should be a pointer");
     static_assert(std::is_same<IntPtr, int*>::value, "IntPtr should be a pointer to int");
     static_assert(std::is_same<IntPtr2, IntPtr>::value, "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<IntAgain>::value, "IntAgain should not be a pointer");
     static_assert(std::is_same<IntAgain, int>::value, "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
                       std::add_pointer was required
   LWG 2101 C++11 to produce Produces cv-/ref-qualified
                       pointer to cv-/ref-qualified function types themselves.
                       function types.

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)