C++: What is std::expected (C++23)?

1#include <expected>
2
3std::expected<int, std::string> divide(int a, int b) {
4    if (b == 0) {
5        return std::unexpected("Division by zero");
6    }
7    return a / b;
8}
9
10auto result = divide(10, 3);
11if (result.has_value()) {
12    std::cout << *result;  // 3
13} else {
14    std::cout << result.error();  // Division by zero
15}
16
17// Chaining with and_then
18auto result2 = divide(10, 2)
19    .and_then([](int val) {
20        return divide(val, 1);
21    });
22
23// Transform value
24auto result3 = divide(10, 2)
25    .transform([](int val) { return val * 10; });
26// result3 = 50
27
28// Value or default
29int val = divide(10, 0).value_or(0);  // 0