Using Subranges vs Iterator Pairs

Using std::ranges::subrange() and standard iterator pairs both allow you to define a specific portion of a range, but they have different use cases and benefits.

Iterator Pairs

Iterator pairs have been a traditional way to define subranges in C++. You specify a range by providing two iterators: a beginning and an end. This method is straightforward and has been widely used:

1#include <algorithm>
2#include <iostream>
3#include <vector>
4
5int main() {
6  std::vector<int> vec{1, 2, 3, 4, 5};
7
8  auto begin = vec.begin() + 1;
9  auto end = vec.begin() + 4;
10
11  std::for_each(begin, end, [](int n) {
12    std::cout << n << ", ";
13  });
14}

12, 3, 4,

std::ranges::subrange

std::ranges::subrange is part of the C++20 ranges library. It provides a more powerful and expressive way to work with subranges. A subrange is a view that encapsulates a pair of iterators and can be used with range-based algorithms seamlessly:

1#include <algorithm>
2#include <iostream>
3#include <ranges>
4#include <vector>
5
6int main() {
7  std::vector<int> vec{1, 2, 3, 4, 5};
8
9  auto subrange = std::ranges::subrange(
10    vec.begin() + 1, vec.begin() + 4);
11
12  std::ranges::for_each(subrange, [](int n) {
13    std::cout << n << ", "; });
14}

12, 3, 4,

Benefits of std::ranges::subrange

1. Readability: std::ranges::subrange makes the code more readable and expressive, clearly indicating that you are working with a subrange of a collection.
2. Range-based Algorithms: It integrates seamlessly with range-based algorithms and views, making it more flexible and powerful.
3. Type Safety: Provides better type safety and prevents common iterator mistakes.

Use Cases

Iterator Pairs is suited for:

• Simple cases where defining the range with iterators is sufficient.
• When working with older codebases that do not use the C++20 ranges library.
• Performance-critical sections where the minimal overhead of raw iterators is beneficial.

std::ranges::subrange is suited for:

• Modern C++ projects that leverage the power of the ranges library.
• Complex operations involving multiple range-based algorithms and views.
• Codebases where readability, maintainability, and expressiveness are prioritized.

In summary, std::ranges::subrange offers a modern and powerful alternative to iterator pairs, enhancing code readability and integration with range-based algorithms.

However, iterator pairs remain a valid and useful tool, especially in simpler or performance-critical contexts.