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Re: Possible bug: sending messages to Class objects


From: Helge Hess
Subject: Re: Possible bug: sending messages to Class objects
Date: Mon, 14 May 2001 10:36:56 +0200

Hi,

Class is a generic type, it can't be used by the type-validator. GNU
ObjC provides no way to statically type a class instance. The only
workaround I know is to define a protocol.

  @protocol MKTuningSystem
  -transpose:(double)semitones
  @end

  id<MKTuningSystem> aTuningClass = [MKTuningSystem class];

Besides that GNU gcc indeed seems to have some problems choosing between
class and instance methods, though I have no sample ready.

Greetings
  Helge

Stephen Brandon wrote:
> 
> Hi,
> 
> Before I go and do a really deep investigation of this problem, I thought I'd 
> throw it to the list
> and see if anyone can point me in the right direction.
> 
> I'm working on the GNUstep port of the SndKit and MusicKit, of NeXTStep fame. 
> Progress is going very
> well on MacOS X...
> 
> Anyway, I am getting the following error when compiling on GNUstep:
> 
> parseScore.m: In function `tune':
> parseScore.m:2825: warning: multiple declarations for method `transpose:'
> /usr/GNUstep/System/Headers/AppKit/NSResponder.h:192: warning: using 
> `-(void)transpose:(id)sender'
> MKTuningSystem.h:190: warning: also found `-transpose:(double)semitones'
> parseScore.m:2825: incompatible type for argument 3 of indirect function call
> 
>                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^    Weird!!!
> 
> The lines in question are:
>         Class aClass = [MKTuningSystem class];
>         [aClass transpose:val];
> 
> (also tried [MKTuningSystem transpose:val]; but that fails in exactly the 
> same way)
> 
> I am comfortable about the fact of a multiple declaration, but I am more 
> concerned that it is
> preventing me from accessing a Class method with the same signature.
> 
> MKTuningSystem has a class method: +transpose: (double)semitones as well as 
> instance method the
> same. If I change the name of the class method, and call the renamed version, 
> then I don't get the
> error, but I don't want to change our API.
> 
> Other info: the parseScore.m file is not actually an objective C class, and 
> the error is inside a
> function not a method.
> 
> More info: running on very latest CVS version of GNUstep, on Caldera 
> OpenLinux 1.3 with lots of
> customisations, gcc --version gives egcs-2.91.66.
> 
> Can anyone shed any light on this? Is it likely to be a compiler error - if 
> so, which version should
> I upgrade to, and are there any tricks to doing so? Any other directions to 
> search in?
> 
> Thanks,
> Stephen Brandon
> address@hidden
> 
> ps I am not on this list: please cc: any replies to me at the above address
> 
> _______________________________________________
> Discuss-gnustep mailing list
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