Casting class to string should raise error

[muglug]

Should be errors:

class A {}
echo (new A);

class A {
    function __toString() : void { }
}
echo (new A);

class A {
    function __toString() { }
}
echo (new A);

should not be an error:

class A {
    function __toString() : string {
        return 'hello';
    }
}
echo (new A);