As far as I'm aware, Object was made different from * in order to make it possible to program without thinking about the 'undefined' value, which Object can't store. It banishes the 'undefined' value from the part of the language that is compile-time-typed, because toher compile-time-typed languages do not have both 'undefined' and 'null'. The Object type requires downcasting because that's normal for all compile-time-types. The * "type" doesn't require downcasting because it isn't a compile-type-type at all. It is simply a notation that tells the compiler "I really want this thing to have no compile time type" as opposed to simply omitting the type annotation, which might mean "I forgot to give this thing a compile-time-type". - Gordon
________________________________ From: flexcoders@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Derek Vadneau Sent: Wednesday, May 23, 2007 9:07 AM To: flexcoders@yahoogroups.com Subject: Re: [flexcoders] star (*) data type vs. Object It's not about getting around compile-time checking, which is what you'd be doing with Object anyhow, I think. Sometimes you really need to dynamically type. In that case, why is Object better than *? Is it for checking null vs. undefined in some cases or is there more to it? On 5/23/07, Peter Farland <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> > wrote: "...but you can't actually type the return variable to anything except Object or nothing." Not true. In your example, you simply need to cast to the correct type, i.e. String: var s:String = go() as String; I don't think using * to get around compile-time type checking is a good idea. You really should be casting values when assigning them from generic types as a best practice. Pete ________________________________ From: flexcoders@yahoogroups.com <mailto:flexcoders%40yahoogroups.com> [mailto: flexcoders@yahoogroups.com <mailto:flexcoders%40yahoogroups.com> ] On Behalf Of Derek Vadneau Sent: Wednesday, May 23, 2007 11:11 AM To: flexcoders@yahoogroups.com <mailto:flexcoders%40yahoogroups.com> Subject: Re: [flexcoders] star (*) data type vs. Object "* 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:pfarland%40adobe.com> <mailto:[EMAIL PROTECTED] <mailto:pfarland%40adobe.com> > > wrote: See: http://livedocs.adobe.com/flex/2/langref/specialTypes.html#* <http://livedocs.adobe.com/flex/2/langref/specialTypes.html#*> <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: flexcoders@yahoogroups.com <mailto:flexcoders%40yahoogroups.com> <mailto:flexcoders% <mailto:flexcoders%25> 40yahoogroups.com <http://40yahoogroups.com> > [mailto: flexcoders@yahoogroups.com <mailto:flexcoders%40yahoogroups.com> <mailto: flexcoders% <mailto:flexcoders%25> 40yahoogroups.com <http://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 -- Derek Vadneau
