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std::same_as

From cppreference.com
< cpp‎ | concepts
 
 
Concepts library
Exposition-only concepts
 (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.

[edit] 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>;

[edit] 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]

[edit] 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]

[edit] See also

(C++11)
checks if two types are the same
(class template) [edit]
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