#include <iostream>
#include <type_traits>
 
// unconstrained template function
auto show(auto x)
{
	std::cout << x << '\n';
}
 
// named requirement
template <typename T> 
concept Number =  std::is_integral_v<T> || std::is_floating_point_v<T>;
 
// constrained template
template <typename T> 
	requires Number<T>
auto show(T x) 
{
	std::cout << "number " << x << '\n';
}
 
// trailing syntax
/*
template <typename T> 
auto show(T x) requires Number<T>
{
	std::cout << "number " << x << '\n';
}
 
// Shorthand syntax
template <Number T> 
auto show(T x) 
{
	std::cout << "number " << x << '\n';
}
*/
 
// terse syntax
Number auto add(Number auto x, Number auto y) { return x+y; }
 
int main()
{
	show(1);
	show("abc");
 
	Number auto x = add(1, 2);     // ok
	Number auto y = add(1, 3.14);  // ok
	// Number auto z = add(1, "3"); // error: char* is not a Number
}