This mixin implements Observer-friendly Array-like behavior. It is not a concrete implementation, but it can be used up by other classes that want to appear like arrays.
For example, ArrayProxy is a concrete class that can be instantiated to implement array-like behavior. This class uses the Array Mixin by way of the MutableArray mixin, which allows observable changes to be made to the underlying array.
This mixin defines methods specifically for collections that provide index-ordered access to their contents. When you are designing code that needs to accept any kind of Array-like object, you should use these methods instead of Array primitives because these will properly notify observers of changes to the array.
You can use the methods defined in this module to access and modify array
contents in an observable-friendly way. You can also be notified whenever
the membership of an array changes by using
EmberArray in your own class, you must override two
primitives to use it: