std::experimental::ranges::identity

C++

Language

Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

Technical specifications

Filesystem library (filesystem TS)

Library fundamentals (library fundamentals TS)

Library fundamentals 2 (library fundamentals 2 TS)

Extensions for parallelism (parallelism TS)

Extensions for parallelism 2 (parallelism TS v2)

Extensions for concurrency (concurrency TS)

Concepts (concepts TS)

Ranges (ranges TS)

Special mathematical functions (special math TR)

Ranges

Concepts

General utilities

Iterators

Ranges

Algorithms

General utilities library

Utility components
swap	exchange
Function objects
invoke identity	equal_to not_equal_to	greater less	greater_equal less_equal
Metaprogramming and type traits
is_swappable_withis_swappable	is_nothrow_swappable_withis_nothrow_swappable	common_reference common_type
Tagged pairs and tuples
TagSpecifier TaggedType	tagged tag specifiers	tagged_pair make_tagged_pair	tagged_tuple make_tagged_tuple

Defined in header <experimental/ranges/functional>
struct identity;		(ranges TS)

ranges::identity is a function object type whose operator() returns its argument unchanged. It is used as the default projection for all Ranges TS algorithms.

Member types

Member type	Definition
is_transparent	/* unspecified */

Member functions

operator()

returns the argument unchanged (public member function)

std::experimental::ranges::identity::operator()

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

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

Parameters

t

-

argument to return

Return value

std::forward<T>(t).

Notes

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.