C++: What is std::ranges::range adaptor composition?

1#include <ranges>
2
3std::vector<int> v = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
4
5// Single adaptor
6auto evens = v | std::views::filter([](int n) { return n % 2 == 0; });
7
8// Composition
9auto result = v
10    | std::views::filter([](int n) { return n % 2 == 0; })
11    | std::views::transform([](int n) { return n * n; })
12    | std::views::take(3);
13// 4, 16, 36
14
15// Reverse
16auto last3 = v | std::views::reverse | std::views::take(3);
17// 10, 9, 8
18
19// Chunk
20auto chunks = v | std::views::chunk(3);
21// [1,2,3], [4,5,6], [7,8,9], [10]
22
23// Flatten
24std::vector<std::vector<int>> nested = {{1,2}, {3,4}, {5,6}};
25auto flat = nested | std::views::join;
26// 1, 2, 3, 4, 5, 6
27
28// Enumerate (C++23)
29for (auto [i, val] : v | std::views::enumerate) {
30    std::cout << i << ": " << val << "\n";
31}
32
33// Common view (for legacy APIs)
34auto common = v | std::views::filter(pred) | std::views::common;
35std::sort(common.begin(), common.end());