The Member Built Before the Throw

1#include <iostream>
2#include <stdexcept>
3 
4class Part {
5public:
6    Part() { std::cout << "part built\n"; }
7    ~Part() { std::cout << "part gone\n"; }
8};
9 
10class Machine {
11    Part m_part;
12public:
13    Machine(bool ok) {
14        std::cout << "machine body\n";
15        if (!ok) {
16            throw std::runtime_error("assembly failed");
17        }
18    }
19    ~Machine() { std::cout << "machine gone\n"; }
20};
21 
22int main() {
23    try {
24        Machine m(false);
25        std::cout << "running\n";
26    } catch (const std::exception& e) {
27        std::cout << "caught: " << e.what() << "\n";
28    }
29    return 0;
30}