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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	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_iden-
       tity (since C++20)

	  template <class T>
	  auto try_add_pointer(int) -> type_identity<typename std::remove_ref-
       erence<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 retroac-
       tively 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)

http://cppreference.com		  2022.07.31		   std::add_pointer(3)

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