I have a interface
`interface Node {...}`
and some classes implementing Node:
```
class Text : Node {...}
class Element : Node {...}
```
and a function like this:
`public void setRelation(ref Node parent , ref Node child) {...}`
if i do this it works:
```
Node root = new Element("root");
Node text = new Text("blah");
setRelation(root , text);
```
but this does not:
```
Node root = new Element("root");
setRelation(root , new Text("blah"));
```
Error: function Nodes.setRelation (ref Node parent, ref Node
child) is not callable using argument types (Node, Text)
Why is this? Text implements Node. This is how i do it in other
Languages - How can would be this possible in D?
