Template Constraints

Template constraints in modern C++ are usually achieved by using concepts, which were introduced in C++20. Concepts provide a way to specify constraints on template parameters. By defining a concept, you can specify the requirements that a type must meet to be used with a template, allowing for clearer and more readable code.

Concepts allow us to specify constraints on template parameters, improving code safety and clarity. Here's how we can use concepts in our templates:

main


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#include <iostream>
#include <concepts> // Include header to use concepts

// Define a concept that requires T to be an integral type
template<typename T>
concept Integral = std::is_integral_v<T>; // The name Integral can be changed

template<Integral T> // Specifying Integral for T
void PrintIntegral(const T& value) { std::cout << value << std::endl; }

int main() {
    PrintIntegral(10);       // Valid: int
    PrintIntegral(20u);      // Valid: unsigned int
    // PrintIntegral(3.14);  // Invalid: won't compile
}

In this example, the Integral concept restricts PrintIntegral to accept only integral types. This is a powerful way to enforce type safety in your code.

Note

Concepts provide meaningful error messages when a type doesn't meet the specified requirements, making debugging easier.

There are numerous concepts available for use, but the most common ones include:

In summary, using concepts in C++ brings a big improvement to template programming. Concepts let you set clear requirements right in the template definition, making your code safer and more readable. By defining what’s needed with concepts, you catch errors at compile time, which saves debugging effort and boosts overall code quality.

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Section 4. Chapter 4