Help - problems with mixin class and recursion

Question

I'm trying to set up functionality which will allow me to track gui node nesting.
Basically, I'd like to have an optional name for each node and be able to generate a string which uses these to track descent. So, e.g., if I have "panel1" as my top scene, "control1" as a node within that scene and "image1" as a node within control1, I'd like to be able to produce the string "panel1.control1.image1" with a call to the image1 node.
I am attempting to do this with a mixin class, as it seems precisely the sort of situation suited to mixins. So I have:
import java.lang*;
public mixin class Descent {
    public-init var objName:String = getClass().toString();
    public function getObjDescent():String;
}When an object is created, it can be assigned a name - or, if there's no assignment, it gets given its class name. When I want the full "descent name" of the object, I'll call getObjDescent(). So far so good.
But now it gets trickier. The idea is to track descent within javafx nodes. If I don't want to assume everything is set up properly, I've got to cover a few cases:
(a) the class into which this object is mixed - the mixee - is not a javafx node
(b) the mixee is a javafx node, but its parent is not
(c) the mixee is a javafx node and descends from a javafx node
Thus:
    public function getObjDescent():String
        var build:String="";
        // get parent's name, if it has it
        try {
            var nodeClass:Class[] = [javafx.scene.Node.class];
            var checkIsNode = this.getClass().getMethod("getNodeMaxHeight",nodeClass);
            if ((this as Node).parent != null) {
                var parentDescentFn = (this as Node).parent.getClass().getMethod("getObjDescent",(null as Class[])) ;
                build = ((this as Node).parent as Descent).getObjDescent();
                build = build.concat(".");
        catch (e:NoSuchMethodException)
            build = "";
        build.concat(this.objName);
    };First I have to check if the mixee is a javafx Node. I can't do this by member checking because javafx doesn't support that. So I have to check by methods. I use one of the Node methods - getNodeMaxHeight - if it is defined for the mixee, the mixee is a node. If not, I'll get an error and can abort down to the catch section.
If this mixee is a node, then it will have a parent node. If that parent also has descent info, I have to prefix that parent's descent name. So now I need to figure out if I can recursively call getObjDescent() on the parent.
So I do the same getMethod() approach on the parent (if any) to see if it has a name I have to prefix. If not then, again, we abort out to the NoSuchMethodException error catch.
Now I should be sure that this is a node and its parent has the Descent fields. So I should be safe to call the parent for its info.
Here I've done this as
((this as Node).parent as Descent).getObjDescent().Though that gives me no errors, I'm not sure if that's the right way to cast things - will it look at the wrong portion of the object to find the method call? Better would be to call the function using the parentDescentFn variable, which I've gotten in checking to see if the parent has the Descent class mixed in, but I can't figure out how to go from a java.lang.reflect.Method variable to generating an actual call of that method. So there's a first question.
However I get to that recursive call, I will get back the parent's descent name. I add my descent separator, '.', and then append the objName of this particular class. Voila - the full descent name.
Though the above throws no warnings in the editor, it generates two compile errors.
First, it tells me it cannot find the symbol:
symbol  : method get$class()
location: class javafx.scene.Node
            var nodeClass:Class[] = [javafx.scene.Node.class];I need to construct a Class[] containing Node for my call to getMethod in the next line. Is this not the right way to specify the Node class?
The next error is:
non-static variable this cannot be referenced from a static context
            var checkIsNode = this.getClass().getMethod("getNodeMaxHeight",nodeClass);I still find what javafx treats as "static" and what non-static to be mystifying. I'm fairly sure I've seen mixin classes which use "this" to grab the mixee object, and I certainly need to do so in this case to check if the mixee is a javafx Node and, subsequently, to get its parent Node.
So... three problems:
- Using "this" in a mixin class ... what's messing that up?
- constructing the Class[] sequence for the first call to getMethod
- (possibly) properly generating a call to the parent mixee's getObjDescent() method.
urg.

Answer 1

RE static vs non-static of this:
I'm not sure, but I think it's a little less straightforward:
e.g. if I type:
var dummy = this; no problem. (This is analogous to what you did.)
But if I type:
var dummy = this.getClass();I get the static/non-static error. I take this to reflect the fact that getClass() is not defined by the mixin class, even if it is defined for any object which might use that class. (Perhaps, down deep in the code, "this" has been redirected to point just to that block of memory which gives the implementation of the mixin information?)
Yet if I type
var dummy = getClass();it works fine, and returns the class which is implementing the mixin.
My guess is that "this" is being treated specially with a mixin class - I think, at compile time, if it just says "this" it is ignored by the "mixin" handling and passed along to the regular class compiling to process, but if it is this.method() or this.member, then the mixin class handles it and will throw that error if it gets any methods or members which it did not itself define.
I haven't had any trouble using the Class objects in javafx, though I don't think I can easily make them do what I, here, specificly want to do. But getClass() seems to work just fine (as long as I don't say this.getClass() !!), as do calls to get or invoke members - I got that one of the 3 problems solved.
I discovered that javafx seems to flatten its classes out to the single implementation of FXObject - when I attempted to parse the interfaces of the mixee class to see if "Node" was a member (which it should be, conceptually), I only got 2 interfaces: FXObject and my mixin class. So I can't use the Class commands to find out of the mixee class object implements Node or not.
I also discovered that, given how javafx seems to compile itself into java, I could actually check for members as well as methods: getMethod("loc$parent") would actually return the parent member, if present. So getMethod can be used to check for the presence of both members and methods in javafx classes. I could not figure out, however, how to get from that reference to the value of the object itself - while invoke() works properly for methods, I couldn't get it to work for the members it retrieved. Though I didn't try too terribly hard.
The getMethod() Class function did allow me to check if a class had my mixin class present - or, at least, if it contained a method with the same name as one defined in that class.
Ultimately, though, I'm still stuck with trying to answer the questions, given a generic javafx class (implicit in this, which I could get by getClass()):
- does this mixee class implement Node?
- if so, what is the value of its "parent" member ((this as Node).parent didn't seem to work within the mixin class' code. Or so it seemed.)
I've gotten around that problem by adding a Node member to the class, so that, rather than trying to deduce it from "this" or the Class functions, it simply uses its variable. Less elegant and more memory-using, but quicker and, actually, more flexible. That approach solves my immediate problem, though it does leave unanswered the more basic questions raised by the exercise.
thanks for the feedback!