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
.
Template parameters
T | - | a type to check |
Helper variable template
template< class T > constexpr bool is_reference_v = is_reference<T>::value; | (since C++17) |
Inherited from std::integral_constant
Member constants
value [static] | true if T is 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> |
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 {}; |
Example
#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
See also
(C++11) | checks if a type is lvalue reference (class template) |
(C++11) | checks if a type is rvalue reference (class template) |
std::experimental::is_reference_v
(library fundamentals TS) | variable template alias of std::is_reference::value (variable template) |
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