// fig15_09.cpp
// Testing custom concepts with static_assert.
#include <iostream>
#include <string>

template<typename T>
concept Numeric = std::integral<T> || std::floating_point<T>;

template<typename T>     
auto multiply(T a, T b) {      
   static_assert(Numeric<T>);      
   return a * b;     
} 

int main() {
   using namespace std::string_literals;
   multiply(2, 5); // OK: int is Numeric
   multiply(2.5, 5.5); // OK: double is Numeric
   multiply("2"s, "5"s); // error: string is not Numeric
} 


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