std::identity (3) - Linux Manuals

std::identity: std::identity


std::identity - std::identity


Defined in header <functional>
struct identity; (since C++20)

std::identity is a function object type whose operator() returns its argument unchanged.

Member types

Member type Definition
is_transparent /* unspecified */

Member functions

           returns the argument unchanged
operator() (public member function)


template< class T>
constexpr T&& operator()( T&& t ) const noexcept;

Returns std::forward<T>(t).


t - argument to return

Return value



The member type is_transparent indicates to the caller that this function object is a transparent function object: it accepts arguments of arbitrary types and uses perfect forwarding, which avoids unnecessary copying and conversion when the function object is used in heterogeneous context, or with rvalue arguments. In particular, template functions such as std::set::find and std::set::lower_bound make use of this member type on their Compare types.


 This section is incomplete
 Reason: no example