std::type_identity

template< class T >
struct type_identity;

Provides the member typedef type that names T (i.e., the identity transformation).

Member types

Helper types

template< class T >
using type_identity_t = typename type_identity<T>::type;

Possible implementation

template< class T >
struct type_identity {
    using type = T;
};

Notes

type_identity can be used to block template argument deduction:

template<class T>
void f(T, T);
 
template<class T>
void g(T, std::type_identity_t<T>);
 
f(4.2, 0); // error, deduced conflicting types for 'T'
g(4.2, 0); // OK, calls g<double>

Example