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std::type_identity

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type_identity
(C++20)
 
Defined in header <type_traits>
template< class T >
struct type_identity;
(since C++20)

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

The behavior of a program that adds specializations for type_identity is undefined.

Contents

[edit] Member types

Name Definition
type T

[edit] Helper types

template< class T >
using type_identity_t = typename type_identity<T>::type;
(since C++20)

[edit] Possible implementation

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

[edit] Notes

type_identity can be used to establish non-deduced contexts in 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>

[edit] Example