C++: What is std::ranges::join_view and std::ranges::split_view?

1#include <ranges>
2
3// join_view — flatten
4std::vector<std::vector<int>> nested = {{1,2}, {3,4}, {5,6}};
5auto flat = nested | std::views::join;
6for (int x : flat) {
7    std::cout << x << " ";  // 1 2 3 4 5 6
8}
9
10// String splitting
11std::string csv = "a,b,c,d";
12auto tokens = csv | std::views::split(',');
13for (auto token : tokens) {
14    std::cout << std::string_view(token) << " ";
15}
16// a b c d
17
18// Split by substring
19std::string text = "one::two::three";
20auto parts = text | std::views::split("::");
21for (auto part : parts) {
22    std::cout << std::string_view(part) << " ";
23}
24// one two three
25
26// Split by predicate
27std::string ws = "hello world  test";
28auto words = ws | std::views::split(std::isspace);
29for (auto word : words) {
30    std::cout << std::string_view(word) << " ";
31}
32// hello world test
33
34// Composable
35auto result = csv
36    | std::views::split(',')
37    | std::views::transform([](auto token) {
38        return std::string_view(token);
39    });