Writing code that operates on ranges of values has become more streamlined and convenient in modern C++. The introduction of the ranges library in C++20 offers a plethora of algorithms and utilities to manipulate collections of elements effectively. One particularly helpful addition is the std::common_range concept, which simplifies the definition of ranges in a concise manner.

What is std::common_range?

std::common_range is a concept specified in the C++20 standard library. It characterizes a type that models both the std::ranges::range and std::ranges::sized_range concepts. In other words, it represents a range that is both iterable and has a known size. The std::common_range concept is enabled for any type that satisfies these requirements.

The std::ranges::range concept ensures that a type can be iterated over, typically through the presence of member functions such as begin() and end(). On the other hand, the std::ranges::sized_range concept adds the capability to determine the number of elements in the range, enabling optimizations based on its size.

Simplifying Range Definitions with std::common_range

The primary advantage of std::common_range is its ability to simplify the definition of ranges without explicitly specifying multiple concepts. By using this concept, we can reduce the verbosity and improve the readability of our code. Here’s an example to demonstrate its usage:

#include <iostream>
#include <ranges>
#include <vector>

void printRangeSize(std::common_range auto&& range)
{
    std::cout << "Range size: " << std::ranges::size(range) << std::endl;
}

int main()
{
    std::vector<int> numbers{1, 2, 3, 4, 5};
    printRangeSize(numbers);
    
    int array[] = {6, 7, 8, 9, 10};
    printRangeSize(array);

    return 0;
}

In the code snippet above, the printRangeSize function takes a parameter range of type std::common_range auto&&. This allows the function to accept any range that models the std::common_range concept, regardless of its specific type.

By using std::common_range, we avoid the need to define separate templates or overloads for different range categories. The std::ranges::size function also works seamlessly with std::common_range, enabling us to retrieve the size of the range regardless of whether it is a container, array, or a custom range type.

Conclusion

The std::common_range concept introduced in C++20 simplifies the definition and handling of ranges in a concise and readable manner. By combining the features of both std::ranges::range and std::ranges::sized_range, it enables us to write more generic and efficient code when working with ranges. Consider leveraging std::common_range in your projects to improve code clarity and maintainability when dealing with ranges.

#cplusplus #rangelibrary