std::same_as

 

C++

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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> subsumes std::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 auto const ... 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)