Re: @dynamic property synthesis

[Ivan Vučica]

Hi David,

On Sunday, August 5, 2012, David Chisnall  wrote:
> Hi Ivan,
>
> Your question is strange because @dynamic is the opposite of @synthesize.  If what you meant was 'can we use declared properties' then the answer is that we've been able to with clang and the GNUstep runtime for ages, and with GCC since 4.6.
>
> There is no such thing as 'runtime-generated @properties', the compiler is responsible for generating these functions, although it does call out to the runtime for some simple cases to avoid burning instruction cache for no reason.  Glancing over the CALayer class reference, they all look like properties that will work with trivial @synthesized implementations.

Most definitely they would.

Except, app developer-supplied CALayer subclasses can define additional animatable properties, then hand them off for run-time synthesis (as opposed to compile time synthesis) via @dynamic.

Similar to what Core Data does: properties are not synthesized at compile time via @synthesize, nor are accessors implemented by the app developer. We could in theory suggest developers to simply @synthesize when compiling for GNUstep (our implementation doesn't distinguish between animatable and non-animatable layer properties), but we should aim for source-level compatibility where possible.

 

> Glancing over your last commit, I can't even begin to work out what you think you are trying to do, but it looks like whatever it is you are not doing it in a sensible way.  Either you are confusing KVC with declared properties, or you don't understand what @dynamic means.  A CoreAnimation implementation does not need these contortions.

Core Animation implementation by itself does not. However, multiple books mention that new animatable properties can be added as described above.

I pretty much would not support this if I designed an API from scratch. However -- if I understood docs correctly, that's the documented way to add new animatable properties. What I did in the commit you're commenting was pretty much the only way I found of adding accessor methods at runtime, and it being so convoluted is the exact reason why I decided to ask for tips.

If someone has worked on adding accessor methods at runtime for properties that were marked with @dynamic, I wouldn't mind help. :-)

More info on what behavior I'm trying to support:

http://stackoverflow.com/questions/2395382/animating-a-custom-property-of-calayer-subclass

and to an extent

http://www.omnigroup.com/blog/entry/Animating_CALayer_content/

-- 
Ivan Vučica - ivan@vucica.net