Puzzle #7 (based on C++17)
Wrong answer. Try again or show the answer.
struct Foo
    Foo(int& baz) 
        : m_baz{ baz }

    void bar() const
        m_baz = 2;

    int& m_baz;

int main()
    int baz{};
    Foo foo{ baz };

    return baz;
With given code, pick one answer:
Guaranteed to return 2 from main
Guaranteed to return something other than 2 from main
Undefined bahaviour
Implementation defined
Will not compile