class Foo {
  Foo* next = nullptr;
public:
  Foo* getNext() { return next; }
  const Foo* getNextConst() const { return next; }

  const Foo &operator= (const Foo &foo) const {
      *this = foo;
      return *this;
  }

  Foo(Foo&) = default;
  Foo& operator=(Foo&) = default;

  Foo() {
  }

private:
  Foo(const Foo&) = default;
  Foo& operator=(const Foo&) = default;
};

int main() {
  // This works as expected
  Foo foo;
  foo.getNext();
  foo.getNextConst();
  // This works as expected too
  const Foo fooConst;
  //fooConst.getNext(); // error!
  fooConst.getNextConst();
  //foo = fooConst; // error!
  // This isn't const-correct, as we can now access the non-const version of Foo.
  foo.getNext();
  foo.getNextConst();
  // This should be possible
  fooConst = foo;
  const Foo fooConst2(foo);

  fooConst = fooConst;
  //const Foo fooConst3 = fooConst; // not supported

  foo = foo;
  Foo foo2(foo);
}