Hi Dave, I see. If this pattern is used inside the Apple Sketch sample (so, in source code you control and not in a framework), then indeed passing a unique Pointer instance should do the trick.
There are probably better ways to do what you want without using the context argument, once you are done with the conversion I can have a look and see if it cannot be written differently :) In any case, we should allow strings and/or symbols to be passed as 'void *' arguments. I will try to implement that later. Thanks for porting this sample! Laurent On May 18, 2010, at 3:05 PM, Dave Baldwin wrote: > Hi Laurent, > > I am converting the Apple Sketch sample app to macruby and this construct is > used everywhere. My understanding (maybe faulty) is all they are trying to > do is generate a unique pointer - pointing at a unique static string should > do this, and by assigning it to a constant will show up compile errors if > spelt wrong. > > The context argument can just be a constant to allow the response to the > observed behaviour to vary or it can be auxiliary information so this makes > sense to me as you might need to know why, how or who caused something > changed, rather than just the fact it has changed. > > In Ruby you would probably just use a symbol, but I presume this would throw > up a run time error like a string does. > > Dave. > > > On 18 May 2010, at 22:36, Laurent Sansonetti wrote: > >> Hi Dave, >> >> Sorry for the late reply. >> >> I'm afraid it's not currently possible to pass a string as an API that >> accepts a 'void *' (which seems to be your case). If you file a ticket on >> the tracker we can address this problem. >> >> Your Pointer.new call may not raise a runtime exception but I suspect it's >> not going to behave correctly later. >> >> I'm not familiar with the API you are using but it seems very uncommon to >> pass constants as context arguments to alter behaviors. Maybe there is >> another way to do what you want? >> >> Laurent >> >> On May 17, 2010, at 2:25 AM, Dave Baldwin wrote: >> >>> Digging a bit more I think a solution to my own questions is: >>> >>> On 13 May 2010, at 14:33, Dave Baldwin wrote: >>> >>>> I am trying to translate code that looks like this: >>>> >>>> static NSString *SKTWindowControllerCanvasSizeObservationContext = >>>> @"com.apple.SKTWindowController.canvasSize"; >>>> >>>> and later >>>> >>>> [[self document] addObserver:self forKeyPath:SKTDocumentCanvasSizeKey >>>> options:NSKeyValueObservingOptionNew >>>> context:SKTWindowControllerCanvasSizeObservationContext]; >>>> >>>> to Ruby: >>>> >>>> SKTWindowControllerCanvasSizeObservationContext = >>>> "com.apple.SKTWindowController.canvasSize" >>> >>> SKTWindowControllerCanvasSizeObservationContext = Pointer.new(:char) >>> >>> as all we are after is a unique value. I still don't understand why the >>> original version wasn't acceptable as the documentation says the context >>> argument can be a C pointer or an object reference. Anyhow, this has got >>> me past this point but I have still to prove the final result when it is >>> used by the observer. >>> >>>> document.addObserver(self, forKeyPath: SKTDocumentCanvasSizeKey, >>>> options: >>>> NSKeyValueObservingOptionNew, >>>> >>>> context:SKTWindowControllerCanvasSizeObservationContext) >>>> >>>> but when it runs I get this error: >>>> >>>> expected instance of Pointer, got >>>> `"com.apple.SKTWindowController.canvasSize"' (String) (TypeError) >>>> >>>> How do I get the a pointer to the context string? All the examples I have >>>> found for the Pointer class seem to expect an objective C routing to fill >>>> it in. >>>> >>>> Thanks, >>>> >>>> Dave. >>>> >>>> >>> >>> Dave. >>> >>> _______________________________________________ >>> MacRuby-devel mailing list >>> MacRuby-devel@lists.macosforge.org >>> http://lists.macosforge.org/mailman/listinfo.cgi/macruby-devel >> >> _______________________________________________ >> MacRuby-devel mailing list >> MacRuby-devel@lists.macosforge.org >> http://lists.macosforge.org/mailman/listinfo.cgi/macruby-devel > > _______________________________________________ > MacRuby-devel mailing list > MacRuby-devel@lists.macosforge.org > http://lists.macosforge.org/mailman/listinfo.cgi/macruby-devel
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