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

0 vote325 views1 answer
C++ check that const char* has suffix
C++
0 vote337 views1 answer
String to decimal c++ strtol
C++
0 vote314 views1 answer
New expression
C++
3 votes318 views2 answers
C++ vector element search
C++
1 vote332 views1 answer
Cmake define standard c++
C++
0 vote333 views1 answer
Pow without math.h
C++
0 vote366 views1 answer
C++ write string
C++
-1 vote343 views1 answer
C++ itoa
C++
0 vote345 views1 answer
Tuple vector c++
C++
0 vote348 views2 answers
344. Reverse String c++
C++