C++20 Concepts Library

 C++20 Concepts Library

C++20 introduced the Concepts library, which provides a standardized way to define and use concepts in C++. Concepts are used to specify requirements for template arguments, improving code clarity, and providing better error messages. The Concepts library defines a set of predefined concepts and also allows users to define their own custom concepts. Here's an example demonstrating the usage of concepts:

#include <iostream>

#include <concepts>

template <typename T>

concept Integral = std::is_integral_v<T>;

template <Integral T>

T square(T value) {

    return value * value;

}

int main() {

    int x = 5;

    double y = 3.5;

    std::cout << "Square of x: " << square(x) << std::endl;

    // Error: square() requires an integral type

    // std::cout << "Square of y: " << square(y) << std::endl;

    return 0;

}

In the above code, we define a custom concept Integral using the std::is_integral_v trait. The concept checks if a type T is integral.

We then define a function template square that takes an argument of type T satisfying the Integral concept. The function calculates the square of the value.

In the main() function, we call square with an int argument, which satisfies the Integral concept. We can print the result. If we try to call square with a double argument, it won't compile because the double type does not satisfy the Integral concept.

The Concepts library provides a standardized way to express requirements and constraints for template arguments, leading to clearer and more robust code.