Defining a Basic Concept

Learn how to define and use concepts to constrain template parameters

Example Code

cpp

#include <concepts>
#include <iostream>
// Define a concept that requires a type to be addable
template<typename T>
concept Addable = requires(T a, T b) {
    { a + b } -> std::convertible_to<T>;
};
// Use the concept to constrain a template
template<Addable T>
T add(T a, T b) {
    return a + b;
}
int main() {
    std::cout << add(5, 3) << std::endl;       // Works: int is Addable
    std::cout << add(2.5, 1.5) << std::endl;   // Works: double is Addable
    // add("hello", "world");  // Error: const char* is not Addable
    return 0;
}

Explanation

Concepts provide a way to specify requirements on template arguments. They replace SFINAE and enable expressions with cleaner, more readable code. The compiler provides better error messages when concept requirements are not met.

Key Points

1Concepts use the 'concept' keyword
2The 'requires' clause specifies type requirements
3Constraints are checked at compile time
4Better error messages than SFINAE