Private vars with Rosy

gistfile1.js

var red = red || {};

red.Module = Class.extend({

    init : function (aVal, bVal) {

        /* All private variables have to live here. */

        var a;
        var b;

        var _Module = Class.extend({

            init : function (aVal, bVal) {
                a = aVal;
                b = bVal;
            },

            log : function () {
                console.log(a, b);
            }

        });

        return new _Module(aVal, bVal);
    }

});


red.SubModule = red.Module.extend({

    init : function (aVal, bVal) {
        this.sup(aVal, bVal);
    }

});


var instance1 = new red.Module("instance1A", "instance1B");
var instance2 = new red.Module("instance2A", "instance2B");


var subInstance1 = new red.Module("subInstance1A", "subInstance1B");
var subInstance2 = new red.Module("subInstance2A", "subInstance2B");


instance1.log(); // Outputs: "instance1A, instance1B"
instance2.log(); // Outputs: "instance2A, instance2B"
subInstance1.log(); // Outputs: "subInstance1A, subInstance1B"
subInstance2.log(); // Outputs: "subInstance2A, subInstance2B"

The downside to this, is that there is additional overhead everytime you create a new instance of Module. There is no way around this if you want your "private"/closured vars on a per instance basis.

Also requires modification of base/class.js (line 62), to:

return this.init.apply(this, arguments);

ah cool - tried it out here and it does work
http://jsfiddle.net/Ktn23/1/