std::same_as

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros(C++20)

Language support library

Concepts library(C++20)

Diagnostics library

Memory management library

Metaprogramming library(C++11)

General utilities library

Containers library

Iterators library

Ranges library(C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library(C++17)

Concurrency support library(C++11)

Execution control library(C++26)

Technical specifications

Symbols index

External libraries

 

Concepts library

Core language concepts same_as (C++20) derived_from (C++20) convertible_to (C++20) common_reference_with (C++20) common_with (C++20) integral (C++20) signed_integral (C++20) unsigned_integral (C++20) floating_point (C++20) swappableswappable_with (C++20)(C++20) destructible (C++20) constructible_from (C++20) default_initializable (C++20)   move_constructible (C++20) copy_constructible (C++20) assignable_from (C++20)

Comparison concepts equality_comparableequality_comparable_with (C++20)(C++20) totally_orderedtotally_ordered_with (C++20)(C++20) Object concepts movable (C++20) copyable (C++20) semiregular (C++20) regular (C++20) Callable concepts invocableregular_invocable (C++20)(C++20) predicate (C++20) relation (C++20) equivalence_relation (C++20) strict_weak_order (C++20)

Exposition-only concepts boolean-testable  (C++20)

 

Defined in header <concepts>
template<class T, class U > concept same_as =/* see below */;		(since C++20)

The concept same_as<T, U> is satisfied if and only if T and U denote the same type.

std::same_as<T, U>subsumesstd::same_as<U, T> and vice versa.

Possible implementation

namespace detail {template<class T, class U > concept SameHelper =std::is_same_v<T, U>;}   template<class T, class U > concept same_as = detail::SameHelper<T, U>&& detail::SameHelper<U, T>;

Example

Run this code

#include <concepts>#include <iostream>   template<typename T, typename ... U> concept either =(std::same_as<T, U>|| ...);   template<typename T> concept is_printable =std::integral<T>||std::floating_point<T>|| either<std::remove_cvref_t<std::remove_pointer_t<std::decay_t<T>>>, char, wchar_t>;   void println(is_printable autoconst ... arguments){(std::wcout<< ... << arguments)<<'\n';}   int main(){ println("Example: ", 3.14, " : ", 42, " : [", 'a', L'-', L"Z]");}

Output:

Example: 3.14 : 42 : [a-Z]

References

• C++23 standard (ISO/IEC 14882:2024):

• 18.4.2 Concept same_as [concept.same]

• C++20 standard (ISO/IEC 14882:2020):

• 18.4.2 Concept same_as [concept.same]

See also

is_same (C++11)

checks if two types are the same (class template)