I'm glad my innocent question has sparked such a fascinating discussion.
I have to admit, from a practical standpoint, it makes it simpler that
Objects can no longer be set to undefined. In AS2, to prevent possible bugs
caused by undefined/null ambiguity, I used to explicitly set my member
variables to null when declaring them. e.g.:
private var _myArray: Array = null;
In AS3, that's no longer necessary.
On a related topic, another feature in AS3 that makes for cleaner code is
the ability to instantiate members when you declare them, e.g.:
private var _myArray: Array = new Array();
This makes me wonder, though, when does instantiation code like that
actually get executed? Does it implicitly happen when the constructor is
called?
ciao,
Adam
On 5/24/07, Troy Gilbert <[EMAIL PROTECTED]> wrote:
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]> wrote:
>
> good post and i agree, dictionaries and arrays should return *
>
> On 5/23/07, Derek Vadneau < [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]> wrote:
> > >
> > > See:
> > >
> > > 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]
<flexcoders%40yahoogroups.com>[mailto:[email protected]<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
>
>
