C++: What is std::views::enumerate (C++23)?

1#include <ranges>
2
3std::vector<std::string> names = {"Alice", "Bob", "Charlie"};
4
5// With index
6for (auto [i, name] : names | std::views::enumerate) {
7    std::cout << i << ": " << name << "\n";
8}
9// 0: Alice
10// 1: Bob
11// 2: Charlie
12
13// Composable
14auto result = names
15    | std::views::enumerate
16    | std::views::filter([](auto pair) {
17        auto [i, name] = pair;
18        return i > 0;
19    });
20
21for (auto [i, name] : result) {
22    std::cout << i << ": " << name << "\n";
23}
24// 1: Bob
25// 2: Charlie
26
27// With transform
28auto indexed = names
29    | std::views::enumerate
30    | std::views::transform([](auto pair) {
31        auto [i, name] = pair;
32        return std::to_string(i) + ". " + name;
33    });
34// "0. Alice", "1. Bob", "2. Charlie"
35
36// vs traditional
37for (size_t i = 0; i < names.size(); i++) {
38    std::cout << i << ": " << names[i] << "\n";
39}