class Foo1 {};
class Foo2 {
public:
    Foo1& operator~() {return foo1;}
private:
    Foo1 foo1;
};
class Foo3 {
public:
    Foo2& T() {return foo2;}
private:
    Foo2 foo2;
};
class Foo4 {
public:
    void bar(const Foo3& f) {foo3 = f;}
private:
    Foo3 foo3;
};