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

1#include <functional>
2
3class Task {
4    std::move_only_function<void()> func;
5public:
6    template<typename F>
7    Task(F f) : func(std::move(f)) {}
8
9    void operator()() {
10        func();
11    }
12};
13
14Task t([] {
15    std::cout << "Running task\n";
16});
17
18Task t2 = std::move(t);  // OK — move-only
19// Task t3 = t;           // Error — not copyable
20
21t2();
22
23// With state
24std::move_only_function<int(int)> add = [x = 10](int y) {
25    return x + y;
26};
27
28std::cout << add(5);  // 15
29
30// Check if empty
31if (add) { add(1); }
32
33// Reset
34add = nullptr;