Instantiate Class using String

In AS2, you could write: attachMovie(“someLibraryItem”, …), and this would create an instance on the _root accessible by _root.someLibraryItem. Is this possible using AS3? I know the standard way is to just do: var foo:LibraryItem = new LibraryItem(), but I’d like to be able to create an instance of a class and have its name be defined by a string. I’d like to do this:

root[“circle” + i] = new MovieClip(); //causes a run-time error

I noticed that the following is still legal in AS3:
trace(root[“circle1”]); //works as expected

Is there any way to do this? I noticed that the “name” property of all DisplayObjects is read-write, but it doesn’t seem that changing the name has any effect on the instance name. Any help would be greatly appreciated!

Andy