C++ Concepts: Improve Type Safety with C++ 20/

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Full Example of Interface

Full Example of Interface

Let's see a complete example of the interface using requirements.

We'll cover the following...

Example with no constraints on the exponent

Let’s have a look at the full example below:

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#include <cmath>
#include <iostream>
#include <string>
#include <concepts>
#include <type_traits>
template <typename Base, typename Exponent>
concept HasPower = std::convertible_to<Exponent, int> &&
                    requires (Base base, Exponent exponent) {
    base.power(exponent);
};
//class having a conversion operator
class IntWithPower {
public:
    IntWithPower(int num) : m_num(num) {}
    int power(IntWithPower exp) {
       return pow(m_num, exp);
    }
    operator int() const { return m_num; }
private:
    int m_num;
};
//function on which concept is applied
template<typename Exponent>
void printPower(HasPower<Exponent> auto number, Exponent exponent) {
    std::cout << number.power(exponent) << '\n';
}
int main() {
    printPower(IntWithPower{5}, IntWithPower{4});
    printPower(IntWithPower{5}, 4L);
    printPower(IntWithPower{5}, 3.0);
}

The concept HasPower expects two template parameters, Base and Exponent, and has two explicit constraints:

  • Using the concept defined on line 8, Exponent
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