std::same_as

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

#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]

is_same (C++11)	checks if two types are the same (class template)
is_same_type (C++26)	checks if two reflections represent the same type (function)

std::same_as

Possible implementation

Example

References

See also