Coercing string to MovieClip class

Question

I've been learning coercion between String and Number and
simple stuff, but now I have a class that the books don't cover.
This is best explained by example (this isn't the end goal, just a
learning example).
On the stage in frame 1, I have a MovieClip instance named
shape_mc.

Answer 1

In your first post you create a variable fubar with no
particular type and then make it a String by concatenating two
other variables. Next you attempt to cast String to MovieClip -
this is what is wrong with the code. Casting works only if an
object somehow is related to other object - in this instance if
fubar data type was related somehow to MovieClip (by extension for
example).
In order to use a string to point to an object - you need to
use an associative array syntax:
parentObject["string"] - given that an object "string" is in
the scope of parentObject.
The following syntax will work (if the movieclip is in the
scope of "this"):
var pre:String="shape";
var suf:String="_mc";
var fubar:* = MovieClip(this[pre + suf]);
Again, the key is to use a correct scope.
As for the flv files, there is no need to cast at all. FLVs
are not MovieClips. It is not clear how you want to play FLVs. Are
they on the server? If so - you need the url to them only (which
are strings). If they are progressive (downloaded via http) your
code may look something like:
var flvURL:String;
function clickListener(e:MouseEvent):void{
flvURL = e.target.name.toString().split("_")[0] + "_flv";
//some time later:
netStream.play(flvURL);
Of course this is just a concept - real code should be
different.