Code Inspection: Possible polymorphic call

Reports polymorphic code usages. Such usages are ambiguous and can be potentially inoperable depending on the class instance passed as the argument.

In the following example, the $property property is only defined in ChildClass but not in ParentClass. As a result, the getProperty() function call is operable when a ChildClass instance is passed as an argument, but inoperable when a ParentClass instance is passed.

class ParentClass {}

class ChildClass extends ParentClass {
    public $property = 1;
}

function getProperty(ParentClass $a) {
    echo $a->property;
}

getProperty(new ChildClass()); //will work, since $property is defined in Child
getProperty(new ParentClass()); //won't work, since $property is not defined in Parent