> don't dictionaries and array effectively return something of type * ?
Yes. I tried
var a:Array = [ undefined ];
trace(a.pop() === undefined);
a = [ undefined ];
trace(a.shift() === undefined);
var s:Sprite = a.pop(); // Object -> Sprite would require a cast
s = a.shift(); // Object -> Sprite would require a cast
var d:Dictionary = new Dictionary();
d["foo"] = undefined;
trace(d["foo"] === undefined);
s= d["foo"]; // Object -> Sprite would require a cast
and the result was
true
true
true
This indicates that Array.pop(), Array.shift(), and Dictionary.[]
actually return * not Object. The hinting and ASDoc are apparently
wrong.
> Gordon, can you speak to what the bytecode difference is between
dynamically typed code and statically typed code?
I don't have details on this but, in general, the player folks recommend
using statically type code when it's possible to do so.
- Gordon
________________________________
From: [email protected] [mailto:[EMAIL PROTECTED] On
Behalf Of Troy Gilbert
Sent: Thursday, May 24, 2007 11:09 AM
To: [email protected]
Subject: Re: [flexcoders] star (*) data type vs. Object
Hmm... don't dictionaries and array effectively return something of type
* ?
In the case of pop(), etc., it wouldn't make sense for the array to
return * because that would mean it _could_ return the value of
undefined, which doesn't make sense. As Gordon points out, Object is
stronger in that it at least indicates existence, even if it is null.
In the case of [ ], isn't the array and dictionary actually returning
something of * type? I know the docs say it's "Object", but it _can_
return undefined, which by definition means it can't be of type "Object"
(undefined has no type).
I'm curious as to the performance implications... I've seen repeated
several times in the docs and blogs that using the strong typing creates
faster code... and I believe it coming from a C++ background where
static types (as opposed to virtual types) are faster because the
compiler can remove some indirection.
But in AS3, and in particular the AVM2, is there similar indirection
being created by the compiler in the bytecode for dynamic types that
doesn't get generated for static types? Gordon, can you speak to what
the bytecode difference is between dynamically typed code and statically
typed code?
Troy.
On 5/23/07, Johannes Nel <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]> > wrote:
good post and i agree, dictionaries and arrays should return *
On 5/23/07, Derek Vadneau < [EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]> > wrote:
"* is just like Object"
I couldn't disagree more.
I really dislike that Object is referred to in the docs
about *. There is an implication there that they are similar when they
really aren't.
This is a sore spot for me everytime I use Array.pop()
and Array.shift() in the Flash IDE. Both of those functions have their
returns typed as Object. Why? Someone thought it was a good idea because
you can have any type returned ... Well, no. Yes, you can have any type
returned at runtime, but you can't actually type the return variable to
anything except Object or nothing.
For example, the Array.as file in the Flash 8 Classes
folder defines:
function shift():Object;
If you try to do this you will get a compiler error:
var arr:Array = new Array(3);
var n:Number = arr.shift(); << compiler error
The same holds true in AS3. For example:
function go():Object
{
return 'something';
}
Everything's valid here. Setting the return type to
Object allows me to return any type that subclasses Object, which is
everything.
var s:String = go(); << compiler error
"Implicit coercion of a value with static type Object to
a possibly unrelated type String."
The compiler doesn't swing that way!
So Object and * are NOT interchangeable. And the
difference isn't subtle.
Use Object when you want to actually use generic objects
and * when you want to dynamically-type something.
On 5/18/07, Peter Farland < [EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]> > wrote:
See:
http://livedocs.adobe.com/flex/2/langref/specialTypes.html#*
<http://livedocs.adobe.com/flex/2/langref/specialTypes.html#*>
The type * is just like Object but it can also
store values that are
undefined. Object can only store null.
It's useful to determine whether a dynamic
property actually exists on a
type and just happens to be null, or whether it
literally is not defined
on that type.
________________________________
From: [email protected]
<mailto:flexcoders%40yahoogroups.com> [mailto:
[email protected] <mailto:flexcoders%40yahoogroups.com> ] On
Behalf Of Adam Pasztory
Sent: Friday, May 18, 2007 2:42 PM
To: flexcoders
Subject: [flexcoders] star (*) data type vs.
Object
Can anyone tell me what the difference is
between setting a generic
variable's data type to Object and setting it to
*. Are they
equivalent?
I tried to search for the answer, but it's hard
to do a search for *. :)
thanks,
Adam
--
Derek Vadneau
--
j:pn
http://www.lennel.org <http://www.lennel.org>
