Can't sleep again. blogged a solution to implementing covariant return types.
http://www.quilix.com/node/17 Rick Winscot From: flexcoders@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Ralf Bokelberg Sent: Thursday, June 26, 2008 9:22 AM To: flexcoders@yahoogroups.com Subject: Re: [flexcoders] AS3 interface question Yep, it's a language feature, which is not there. I think it is called covariant return types. Afaik, all you can do is check the type and cast. Cheers Ralf. On Thu, Jun 26, 2008 at 3:14 PM, diehlryan <[EMAIL PROTECTED] <mailto:rdiehl%40docfinity.com> > wrote: > I'm running into a wall when trying to use extension with interfaces. > The example I'm about to provide works using Java, so I believe the > OOP practices behind it are valid. But I can't figure out how to > accomplish the same thing in Flex, I keep running into compiler > issues. The example is a condensed version of something I'm working > on, for simplicity sake. > > Let's say you have a bunch of events that all have some common > functionality, like the ability to have a nextEvent. Also, a subset > of those events also have additional functionality, they can be > filtered by a type of criteria. We'll call them search events. > > Now, there are some parts of the application that can work with any > type of search event, and any type of criteria. But when the > individual searches are executed, that implementation expects a > specific type of search event and search criteria. That's my end goal > here. > > Here are the interfaces I'm using: > > public interface ICriteria > { > // just a marker > } > > public interface ICustomCriteria extends ICriteria > { > function get name():String; > function set name(name:String):void; > } > > public interface IEvent > { > function get nextEvent():IEvent; > function set nextEvent(event:IEvent):void; > } > > public interface ISearchEvent > { > function get criteria():ICriteria; > function set criteria(criteria:ICriteria):void; > } > > So far, so good. And now the implementing classes: > > // would like to make this an abstract class, but not supported in AS > public class BaseEvent implements IEvent > { > private var _nextEvent:IEvent; > > public function set nextEvent(event:IEvent):void > { > this._nextEvent = event; > } > > public function get nextEvent():IEvent > { > return this._nextEvent; > } > } > > // would like to make this an abstract class, but not supported in AS > public class BaseSearchEvent extends BaseEvent implements ISearchEvent > { > private var _criteria:ICriteria; > > public function set criteria(criteria:ICriteria):void > { > this._criteria = criteria; > } > > public function get criteria():ICriteria > { > return this._criteria; > } > } > > Those base classes are fine and compile correctly. Now if you > remember from the requirements, there are some places that can work > with any type of ISearchEvent, and some places that can only work with > an individual subclass. Here is where the compiler errors come in. > Doing what I am about to do works in Java, and I'm wondering if there > is a way to accomplish it in AS3. > > public class CustomSearchEvent extends BaseSearchEvent > { > private var _criteria:ICustomCriteria; > > public override function get criteria():ICustomCriteria > { > return this._criteria; > } > > public override function set criteria(criteria:ICustomCriteria):void > { > this._criteria = criteria; > } > } > > The above class does not compile because the method signatures for > get/set criteria are different than those specified in the interface. > But from an OO perspective, I think this is a valid thing to want to > do. If you're working with an ISearchEvent instance, you should be > able to subclass the base class and provide custom behavior. The > ICustomCriteria is a subclass of ICriteria, so you should be able to > substitute them in this context. Is there another way to accomplish > this? Or is this just a language feature that's not there? > >
