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I want to implement multiple inheritance using google closure. I have already researched and I found this book. At page 158, they say that google closure doesn't support multiple inheritance, but that there are other ways to do it, like using "goog.mixin". I tried it but I get "Uncaught AssertionError: Failure".

Basically, I want to do something like this:

class A {
    function moveLeft() {
        ...
    },
    function moveRight() {
        ...
    }
}

class B extends A {
    function moveTop() {
        ...
    }
}

class C extends B {
    function moveBottom() {
        ...
    }
}
  • Class A has the methods "moveLeft" and "moveRight".
  • Class B has the methods "moveLeft", "moveRight" AND "moveTop" (normal inheritance, gets the methods from the parent class A)
  • Class C should have the methods "moveLeft", "moveRight", "moveTop" AND "moveBottom" (double inheritance, gets the methods from the parent class B, and the grandparent class A)

BUT class C only gets the methods of class B the way I am doing.

How could I do this using google closure?

Thank you.

João

EDIT 1

I will try to make myself clearer. I can't display here the whole code for professional reasons. This is a bit how my classes look like.

// external file xgis.js

xgis = {};


// xgis.map
xgis.map = function(options) {
    // map definitions ...
};
// Inherits from ol.Map
goog.inherits(xgis.map, ol.Map);


// xgis.layer
xgis.layer = function(options) {
    // base layer definitions
};


// xgis.layer.osm
xgis.layer.osm = function(options) {
    goog.base(this, {
        source: new ol.source.OSM()
    });
    sigga.layer.call(this, options);
};
// Inherits from ol.layer.Tile
goog.inherits(xgis.layer.osm, ol.layer.Tile);
/**
 * Copies all the members of a source object to a target object.
 * i.e, inherits ALSO from xgis.layer (the base layer class)
 */
goog.mixin(xgis.layer.osm.prototype, xgis.layer.prototype);

The goal is to build an SDK, which I named here "xgis". We want to build our API on top of OpenLayers 3 (ol3). We want our own methods to use the ol3 methods. We need to have our own method for documenting.

For example, I want my own method to check the visibility of a layer. But this method has to use the one from ol3 "with the same name as mine":

// My method
xgis.layer.prototype.getVisible = function() {
    // Used the method of the parent class from ol3
    return this.superClass_.getVisible();
};

I tried to use the keyword "superClass_" to get the method of the parent class, but it didn't work.

Is there another way?

joaorodr84
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  • A couple of things that will help clarify things: 1) what is the failure you see (build time, runtime)? 2) on what object is "getVisible" defined 3) how it defined? - Make sure xgis.layer.osm is declared as constructor - Make sure xgis is declared as const - Makre sure xgis.lay is either const or constructor as appropriate – John May 27 '14 at 16:51
  • Hi @John. First of all, thank you for your answer. I'll try to clarify things. ... 1) my own xgis.layer.prototype.getVisible() cannot be defined, because I already have the "getVisible" method from the parent (because of the xgis.layer inherits it from ol.layer.Tile) ... 2) The inner getVisible comes from ol.layer.Tile; my own xgis.layer.prototype.getVisible can't be defined as I said in (1). I want my getVisible to be defined in xgis.layer! ... 3) I don't really understand what you mean, but I intend to define getVisible as prototype from the class xgis.layer. ... Thanks again. – joaorodr84 May 27 '14 at 17:55

1 Answers1

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Can you write your example as valid JavaScript? As far as I can tell this isn't "multiple inheritance" but simply multiple levels of inheritance.

I think you mean:

function A() {}
A.prototype.moveLeft = function() {};

function B() {}
goog.inherits(B, A);
A.prototype.moveTop = function() {};

function C() {}
goog.inherits(C, B);
A.prototype.moveBottom = function() {};
John
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  • Hello @John. I added some JavaScript code, in the hope that you could offer some more help. Check out EDIT 1, please. Thanks. :) – joaorodr84 May 26 '14 at 12:07
  • with goog.mixin the type system doesn't understand it although the optimization should be fine. There can only be one value for superClass_ however so you need to call the super class explicitly: ol.layer.Tile.prototype.getVisible.call(this) – John Jun 03 '14 at 17:26