AS3: cast or “as”?

Question

Is there any difference of use, efficiency or background technique between

var mc:MovieClip = MovieClip(getChildByName(\"mc\"));

and

<

Answer 1

var mc:MovieClip = MovieClip(getChildByName("mc"));

will DIRECTLY SET IT AS movieclip

var mc:MovieClip = getChildByName("mc") as MovieClip;

will make mc act like a movieclip, if required type are same