Using std::ranges Algorithms with Container Views

std::ranges algorithms work seamlessly with container views like std::span and std::string_view, providing a flexible way to operate on sub-ranges or specific sections of data without copying it.

Using std::span

std::span is a non-owning view over a contiguous sequence of elements. Here’s an example using std::ranges::count() with std::span:

1#include <algorithm>
2#include <iostream>
3#include <span>
4#include <vector>
5
6int main() {
7  std::vector<int> numbers {1, 2, 3, 4, 4, 5};
8  std::span<int> numbersView(
9    numbers.data(), numbers.size());
10
11  auto foursCount = std::ranges::count(
12    numbersView, 4); 
13  std::cout << "Count of fours: " << foursCount;
14}

1Count of fours: 2

Using std::string_view

std::string_view provides a view over a string without owning the actual string data. Here's an example using std::ranges::count() with std::string_view:

1#include <algorithm>
2#include <iostream>
3#include <string>
4#include <string_view>
5
6int main() {
7  std::string text = "hello world";
8  std::string_view textView(text);
9
10  auto lCount = std::ranges::count(textView, 'l');  
11  std::cout << "Count of 'l': " << lCount;
12}

1Count of 'l': 3

Benefits

• Efficiency: Views avoid copying data, leading to more efficient code.
• Flexibility: They allow operations on subsections of containers.
• Safety: Views can be safely used without worrying about managing the underlying data's lifetime.

Practical Usage

• Sub-ranges: Use views to process parts of a container.
• Read-only Access: std::string_view is great for read-only string operations.
• API Design: Pass views to functions to make them more versatile.

By using container views with std::ranges algorithms, you can write efficient, flexible, and clear code. This approach is particularly useful in modern C++ for handling large datasets and optimizing performance.