home | help 
std::is_same(3) 	       C++ Standard Libary		 std::is_same(3)

NAME
     std::is_same - std::is_same

Synopsis
	Defined in header <type_traits>
	template< class T, class U >	 (since C++11)
	struct is_same;

	If T and U name the same type (taking into account const/volatile quali-
     fications),
	provides  the  member  constant  value equal to true. Otherwise value is
     false.

	Commutativity is satisfied, i.e. for any two types T and  U,  is_same<T,
     U>::value ==
	true if and only if is_same<U, T>::value == true.

	If the program adds specializations for std::is_same
	or std::is_same_v
	(since C++17), the behavior is undefined.

Member constants
	value	 true if T and U are the same type, false otherwise
	[static] (public static member constant)

Member functions
	operator bool converts the object to bool, returns value
		      (public member function)
	operator()    returns value
	(C++14)       (public member function)

Member types
	Type	   Definition
	value_type bool
	type	   std::integral_constant<bool, value>

Possible implementation
	template<class T, class U>
	struct is_same : std::false_type {};

	template<class T>
	struct is_same<T, T> : std::true_type {};

Example
     // Run this code

      #include <cstdint>
      #include <iostream>
      #include <type_traits>

      int main()
      {
	  std::cout << std::boolalpha;

	  // some implementation-defined facts

	  // usually true if 'int' is 32 bit
	  std::cout  <<  std::is_same<int, std::int32_t>::value << ' '; // maybe
     true
	  // possibly true if ILP64 data model is used
	  std::cout << std::is_same<int, std::int64_t>::value << ' ';  //  maybe
     false

	  // same tests as above, except using C++17's std::is_same_v<T, U> for-
     mat
	  std::cout << std::is_same_v<int, std::int32_t> << ' ';  // maybe true
	  std::cout << std::is_same_v<int, std::int64_t> << '\n'; // maybe false

	  // compare the types of a couple variables
	  long double num1 = 1.0;
	  long double num2 = 2.0;
	  static_assert(  std::is_same_v<decltype(num1), decltype(num2)> == true
     );

	  // 'float' is never an integral type
	  static_assert( std::is_same<float, std::int32_t>::value == false );

	  // 'int' is implicitly 'signed'
	  static_assert( std::is_same_v<int, int> == true );
	  static_assert( std::is_same_v<int, unsigned int> == false );
	  static_assert( std::is_same_v<int, signed int> == true );

	  // unlike other types, 'char' is neither 'unsigned' nor 'signed'
	  static_assert( std::is_same_v<char, char> == true );
	  static_assert( std::is_same_v<char, unsigned char> == false );
	  static_assert( std::is_same_v<char, signed char> == false );

	  // const-qualified type T is not same as non-const T
	  static_assert( !std::is_same<const int, int>() );
      }

Possible output:
      true false true false

See also
	same_as 		  specifies that a type is the same  as  another
     type
	(C++20) 		  (concept)
	decltype specifier(C++11) obtains the type of an expression or an entity

http://cppreference.com 	   2024.06.10			 std::is_same(3)
home | help