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std::add_pointer(3)	      C++ Standard Libary	   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	behav-
       ior 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::re-
       move_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 retroac-
       tively to
	  previously published C++ standards.

	     DR	   Applied to	      Behavior as published		  Cor-
       rect 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)

http://cppreference.com		  2024.06.10		   std::add_pointer(3)

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