C++ require keyword

#include <string>
#include <cstddef>
#include <concepts>
 
// Declaration of the concept "Hashable", which is satisfied by any type 'T'
// such that for values 'a' of type 'T', the expression std::hash<T>{}(a)
// compiles and its result is convertible to std::size_t
template<typename T>
concept Hashable = requires(T a) {
    { std::hash<T>{}(a) } -> std::convertible_to<std::size_t>;
};
 
struct meow {};
 
// Constrained C++20 function template:
template<Hashable T>
void f(T) {}
//
// Alternative ways to apply the same constraint:
// template<typename T>
//    requires Hashable<T>
// void f(T) {}
//
// template<typename T>
// void f(T) requires Hashable<T> {}
 
int main() {
  using std::operator""s;
  f("abc"s); // OK, std::string satisfies Hashable
//f(meow{}); // Error: meow does not satisfy Hashable
}

Source: en.cppreference.com

Similar codes

1 vote129 views2 answers
How to get size of char array in c++
C++
0 vote119 views1 answer
How to check char array equality in c++
C++
-1 vote133 views3 answers
Iff cpp
C++
2 votes169 views1 answer
Check gpu usage jetson nano
C++
0 vote141 views1 answer
Could not load the Visual C++ component "VCBuild.exe". To fix this, 1) install the .NET Framework 2.0 SDK, 2) install Microsoft Visual Studio 2005 or 3) add the location of the component to the system path if it is installed elsewhere.
C++
0 vote163 views1 answer
Passing custom function in sort cpp
C++
1 vote119 views1 answer
Terminal compile c++
C++
19 votes122 views3 answers
Segmentation fault (core dumped)
C++
0 vote152 views1 answer
C++ find index of all occurrences in string
C++
4 votes127 views2 answers
Double max value c++
C++