What's difference between constructor and as operator?

[sinwi]

Hi, all~

Sometimes a property returns value as "super" as the class related. For a simple example: a child call its parent MovieClip to .stop(); However, this.parent property returns a DisplayObjectContainer which has no such method. At this time, I like to use (parent as MovieClip).stop(); to "treat him as" a MovieClip, because I think its already a MovieClip, there's no need to "convert". But I noticed that many people and many examples in the reference and documents use the constructor, like: MovieClip(parent).stop(); even the constructor do not receive a parameter. I'm wondering what's the difference between them, and which is better?

Am I entanglement? Thanks~~~~

[kglad · Accepted solution]

that's not using the constructor.  nothing is being created or constructed when you use MovieClip(child.parent).

you are casting the child.parent as a MovieClip.  that can only be done if child.parent already is a MovieClip and the only reason you need to do that is because the flash compiler doesn't have a terrific memory.  it easily forgets that a child with a MovieClip parent is a MovieClip. 

the compiler knows every child has a DisplayObjectContainer parent but it often forgets if that parent is a MovieClip or a Sprite or a Loader or the stage etc.  so, if you fail to cast the parent as a MovieClip the compiler can (erroneously) complain that you're using an illegal method and/or you're implicitly casting a DisplayObjectContainer as a MovieClip.

explicitly casting as a MovieClip makes the compiler happy.