C++: What is std::ranges::cache_latest (C++26)?

1#include <ranges>
2
3std::vector<int> v = {1, 2, 3, 4, 5};
4
5// Without cache (re-evaluates on each access)
6auto transform_view = v
7    | std::views::transform([](int x) {
8        std::cout << "Computing " << x << "\n";
9        return x * x;
10    });
11
12// With cache (evaluates once)
13auto cached = v
14    | std::views::transform([](int x) {
15        std::cout << "Computing " << x << "\n";
16        return x * x;
17    })
18    | std::views::cache_latest;
19
20// Multiple reads only compute once
21auto it = cached.begin();
22std::cout << *it;  // Computing 1
23std::cout << *it;  // No re-computation
24std::cout << *it;  // No re-computation
25
26// Useful for expensive computations
27auto primes = std::views::iota(2)
28    | std::views::transform([](int n) {
29        // Expensive primality test
30        return is_prime(n) ? std::optional(n) : std::nullopt;
31    })
32    | std::views::filter([](auto opt) { return opt.has_value(); })
33    | std::views::transform([](auto opt) { return *opt; })
34    | std::views::cache_latest;
35
36// Iterate primes
37for (int p : primes | std::views::take(10)) {
38    std::cout << p << " ";
39}