Multiple inheritence: combining VerletParticle() with WB_Point()

Processing.py
1

Hi all,

I’m working on a sketch where a Cell class needs to inherit both from Toxiclibs’ VerletParticle() and Hemesh WB_Point(). Ideally I would like the Cell object to share specific attributes from the two libraries (WB_Point connected by VerletSprings).

Is that possible in Python mode ?

With other Processing libraries I used to write something like this:

class Cell(VerletParticle2D, Locatable):
    def __init__(self, x, y):
        super(Cell, self).__init__(x, y)
        self.isActive = False
        
    def getLocation(self):
        return PVector(self.x(), self.y())

but this time, class Cell(VerletParticle2D, WB_Point) returns the following error:

processing.app.SketchException: TypeError: Error when calling the metaclass bases no multiple inheritance for Java classes: toxi.physics2d.VerletParticle2D and wblut.geom.WB_Point
at jycessing.mode.run.SketchRunner.convertPythonSketchError(SketchRunner.java:242)
at jycessing.mode.run.SketchRunner.lambda$2(SketchRunner.java:119)
at java.lang.Thread.run(Thread.java:748)

Is there a way to get around this error ?

1 Like
2

Which library does Locatable come from? Surely it’s an interface, not a Java class, right?

Java can implement multiple interfaces; but can only extend 1 class!

Jython, just like Python, can inherit from multiple Python classes, creating a mixin among them.

However, when it’s a Java class, Jython can only inherit 1!

Given you can pick 1 only, as a poor workaround, you can make the other Java class become a property of the picked 1:

class Cell(VerletParticle2D):
    def __init__(c, *args):
        super(Cell, c).__init__(*args)
        c.wb_p = WB_Point(*args)
        c.isActive = False

In the subclass above, VerletParticle2D was chosen as the parent Java class, while WB_Point became 1 of its new properties as wb_p.

I’m not sure, but I believe you might want properties x & y to be the same for both VerletParticle2D & WB_Point, right?

Anyways, I’ve made methods makeVerletEqualPoint() & makePointEqualVerlet() as another poor workaround:

add_library('toxiclibs')
add_library('hemesh')

def setup():
    print VerletParticle2D, WB_Point, ENTER

    global cell
    cell = Cell(random(10), random(10))
    print cell, ENTER, cell.wb_p, ENTER

    print cell.wb_p.scaleSelf(random(5))
    print cell.makeVerletEqualPoint(), ENTER

    print cell.scaleSelf(random(5))
    print cell.makePointEqualVerlet()

    exit()


class Cell(VerletParticle2D):
    def __init__(c, *args, **kws):
        super(Cell, c).__init__(*args, **kws)
        c.wb_p = WB_Point()
        c.makePointEqualVerlet()
        c.isActive = False


    def makeVerletEqualPoint(c):
        return c.set(c.wb_p.x, c.wb_p.y)


    def makePointEqualVerlet(c):
        c.wb_p.set(c.x(), c.y())
        return c.wb_p
3 Likes
3

Thank you for the reply and detailed explanations (as always!).

Locatable comes from the GiCentre library and is indeed an interface, my bad.

I ended-up with the same workaround you’re suggesting and it works “ok” so far. I guess I’ll stick with this solution for now.

Thanks again

4

The other option is composition. Have your new class simply contain an instance each of the two class objects, and your container class will map their interfaces out as needed / keep them in sync.

1 Like