addcomponent, question about 'AS'

Unity Engine
1

Hello everybody,

in many javascript example I’ve found two ways of calling AddComponent:

g.AddComponent(Rigidbody);

or
g.AddComponent(Rigidbody) as Rigidbody;

or

g.AddComponent(“Rigidbody”) as RigidBody;

so no matters what component I’m adding, what’s the difference in using the keyword AS and not using it?

Cheers,
Giancarlo

2

You’re going to see “as” mostly when you’re using the result of AddComponent. Since AddComponent returns a component, you need to declare that you want what’s returned to be “Typecast” to a Rigidbody. Otherwise, if you did something like

var myRigidbody = gameObject.AddComponent(Rigidbody);
myRigidbody.mass = 10;

It will fail, because “mass” is not a field in Component. An easy way around this problem is to use the recently-added-to-Javascript generic version of AddComponent, ie. gameObject.AddComponent.<Rigidbody> ();

3

In this case, “as” attempts to cast the result as a RigidBody. IF the returned object is not actually a RigidBody, the result of the operation will be a null value. If you explicitly cast it: RigidBody(g.AddComponent(“RigidBody”)), and the result isn’t a RigidBody, it will throw an exception.

Specifically talking about your examples:

  1. This returns a type “Object”, so you can’t directly call any of the members on RigidBody until you cast it.

  2. This is fairly type-safe (but not at compile-time), AddComponent won’t return a non-RigidBody since you explicitly give it the type. It sill requires a run-time cast though.

  3. Technically, this isn’t so type-safe since you just pass in a string, and as far as the letter of the law in code is concerned, could possibly not return a RigidBody (more likely you would typo the “RigidBody” string, whereas in example 2, you can’t typo it; it won’t%

4

Oky doky! I think I’ve understand now… yeah, thanks a lot!!! :)))

5

Odd, I had posted also the usage of generics and credited burnumd for beating me to it, but the post cut it off at that % sign.

;_;

Glad we could help!

6

Curious! :frowning:

btw… where is the button that says “SOLVED” ?

7

There isn’t, but you can edit your opening post to indicate that.

8

I actually saw that part in the notification email I got about the thread, but yeah, it’s weird.