std::is_reference
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | Defined in header  <type_traits> | ||
| template< class T > struct is_reference; | (since C++11) | |
If T is a reference type (lvalue reference or rvalue reference), provides the member constant value equal true. For any other type, value is false.
| Contents | 
[edit] Template parameters
| T | - | a type to check | 
[edit] Helper variable template
| template< class T > inline constexpr bool is_reference_v = is_reference<T>::value; | (since C++17) | |
Inherited from std::integral_constant
Member constants
| value [static] | true if Tis a reference type , false otherwise(public static member constant) | 
Member functions
| operator bool | converts the object to bool, returns value(public member function) | 
| operator() (C++14) | returns value(public member function) | 
Member types
| Type | Definition | 
| value_type | bool | 
| type | std::integral_constant<bool, value> | 
[edit] Possible implementation
| template <class T> struct is_reference : std::false_type {}; template <class T> struct is_reference<T&> : std::true_type {}; template <class T> struct is_reference<T&&> : std::true_type {}; | 
[edit] Example
Run this code
#include <iostream> #include <type_traits> class A {}; int main() { std::cout << std::boolalpha; std::cout << std::is_reference<A>::value << '\n'; std::cout << std::is_reference<A&>::value << '\n'; std::cout << std::is_reference<A&&>::value << '\n'; std::cout << std::is_reference<int>::value << '\n'; std::cout << std::is_reference<int&>::value << '\n'; std::cout << std::is_reference<int&&>::value << '\n'; }
Output:
false true true false true true
[edit] See also
| (C++11) | checks if a type is lvalue reference (class template) | 
| (C++11) | checks if a type is rvalue reference (class template) | 


