Classes should not be allowed to shadow non-private instance variables from their base:

class Parent
{
    int x = 1;
}
class Child: Parent
{
    int x = 3;
}
void main()
{
    Child child = new Child();
    Parent parent = child;

    assert(parent is child);       // same object
    assert(parent.x != child.x);   // different value for member x
}