C++: What is std::ranges::cartesian_product (C++23)?

1#include <ranges>
2
3std::vector<int> v1 = {1, 2};
4std::vector<char> v2 = {'a', 'b', 'c'};
5
6auto product = std::views::cartesian_product(v1, v2);
7
8for (auto [x, y] : product) {
9    std::cout << "(" << x << ", " << y << ") ";
10}
11// (1, a) (1, b) (1, c) (2, a) (2, b) (2, c)
12
13// Size is product of sizes
14std::cout << product.size();  // 6
15
16// Three ranges
17std::vector<int> v3 = {10, 20};
18auto prod3 = std::views::cartesian_product(v1, v2, v3);
19for (auto [x, y, z] : prod3) {
20    std::cout << "(" << x << "," << y << "," << z << ") ";
21}
22// (1,a,10) (1,a,20) (1,b,10) (1,b,20) (1,c,10) (1,c,20)
23// (2,a,10) (2,a,20) (2,b,10) (2,b,20) (2,c,10) (2,c,20)
24
25// Lazy evaluation
26auto first_few = product | std::views::take(3);
27for (auto [x, y] : first_few) {
28    std::cout << "(" << x << ", " << y << ") ";
29}
30// (1, a) (1, b) (1, c)
31
32// Nested for loop replacement
33for (auto [i, j] : std::views::cartesian_product(
34    std::views::iota(0, 3),
35    std::views::iota(0, 3))) {
36    std::cout << "(" << i << "," << j << ") ";
37}