std::type_identity - cppreference.com
From cppreference.com
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(since C++20) | |
Provides the member typedef type that names T (i.e., the identity transformation).
If the program adds specializations for std::type_identity, the behavior is undefined.
Member types
Helper types
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(since C++20) | |
Possible implementation
template<class T> struct type_identity { using type = T; };
Notes
std::type_identity can be used to establish non-deduced contexts in template argument deduction.
| Feature-test macro | Value | Std | Feature |
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__cpp_lib_type_identity |
201806L |
(C++20) | std::type_identity
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Example
#include <iostream> #include <type_traits> template<class T> T foo(T a, T b) { return a + b; } template<class T> T bar(T a, std::type_identity_t<T> b) { return a + b; } int main() { // foo(4.2, 1); // error, deduced conflicting types for 'T' std::cout << bar(4.2, 1) << '\n'; // OK, calls bar<double> }
Output:
See also
| function object that returns its argument unchanged (class) [edit] |