On Feb 24, 2011, at 3:58 AM, Andreas Grosam wrote: >> You can't, but you can declare protocols for your ObjC++ classes in separate >> headers then have the ObjC classes interact with "NSObject<Foo>" instead of >> Foo objects directly. >> >> FooProtocol.h >> >> @protocol Foo >> // methods the pure ObjC classes need to see >> @end >> >> Foo.h >> >> #import "FooProtocol.h" >> @interface Foo : NSObject <Foo> >> ... >> >> Foo.mm >> #import "Foo.h" >> // do C++ things here >> >> Bar.m >> >> #import "FooProtocol.h" >> // do things with NSObject<Foo> > This would be an excellent approach, since protocols are the real and pure > interfaces -- like "formal" duck-typing :) > > However, with protocols alone you cannot create objects - you need some sort > of factory method, declared in some other class: > > id<Foo> myFooObject = [someObject newFoo]; > > Note: someObject can be a class object or an instance object. It just needs > to implement the factory methods. The resulting object can be an instance of > any class, it doesn't need to be class Foo.
You can use protocols alone to do object creation with a little runtime trickery. I'm quite fond of this small set of language "extensions": <http://code.google.com/p/libextobjc/> For this situation, I was thinking of the "concrete protocol" implementation provided by the library, which I've used several times to plug functionality into classes when I couldn't change the inheritance. Other languages call these traits. (And while on the subject of language extensions, I also shamelessly plug for Michael Ash's MAGenerator class. +1 to get both that and libextobjc constructs into Objective-C 3.) -- Gwynne _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
