mixin.js

    SC.Enumerable = SC.Mixin.create({
      forEach: SC.Mixin.required(),
      
      init: SC.Mixin.concat(),
      destroy: SC.Mixin.concat(),
      
      map: function(f, ctx) {
        var ret = [];
        if (!ctx) ctx = this;
        this.forEach(function(x) { ret.push(f.call(ctx,x)); });
        return ret;
      },
      
      contains: function() { ... }
      
    });

    // add more properties to a trait later on
    SC.Enumerable.mixin({
      filter: function() { .. }
    });
    
    // ensures that all SC.Array's are also enumerables
    SC.Array = SC.Mixin.create(SC.Enumerable, {
      objectAt: function() { ... },
      contains: function() { ... }
    });

    // wot!  both Array and Enumerable define contains.  Use the without
    // operation:
    SC.Array = SC.Mixin.create(SC.Enumerable.without('contains'), {
    
    });

    // but what if we still want the Enumerable contains?
    SC.Array = SC.Trait.create(
      SC.Enumerable.rename({ contains: '_enumerableContains' }), {
      // array properties here...
    });
    
    // you can apply a mixin to any object instance.
    SC.Array.apply(Array.prototype);
    
    // You can also build objects the same way
    SC.Set = SC.Object.extend(SC.Enumerable, { ... });
    myView = SC.View.create(SC.Bordered, { .. })