var inheritance = {

    extend:function(sub, sup){
        var Fn = function(){
            // empty
        };

        Fn.prototype = sup.prototype;
        sub.prototype = new Fn();
        sub.prototype.constructor = sub;

        sub.superclass = sup.prototype;
        if(sup.prototype.constructor == Object.prototype.constructor){
            sup.prototype.constructor = sup;
        }
    }

};