Re: BUG?: Multiple Inheritance and DO

FROM : Philip Mötteli
DATE : Mon Apr 25 19:37:36 2005

Am 25.04.2005 um 18:45 schrieb Aurélien Hugelé:
> On 24 avr. 05, at 23:58, Philip Mötteli wrote:

>> Has Apple changed something with their implementation of Distributed 
>> Objects? Do they always call -methodDescriptionForSelector: before 
>> calling the real method?
>> I have an object, that implements multiple inheritance. I have done 
>> this, by implementing the following methods:
>>
>> - (void)forwardInvocation:(NSInvocation *)anInvocation;
>> - (BOOL)respondsToSelector:(SEL)aSelector;
>> - (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector;
>>
>> So far everything worked well. But since recently, I see the 
>> NSConnection make the following call, before calling the real method:
>>
>> -[anObject 
>> methodSignatureForSelector:@selector(methodDescriptionForSelector:)]
>>
>>
>> Of course this returns something, because 
>> -methodDescriptionForSelector: is implemented by Apple in NSObject. 
>> But then in this method they seem to try to extract some information 
>> about the real method, that was called. Unfortunately, the real 
>> method is not part of the original object, but part of the multiple 
>> inheritance, so another object. So I get a 'method not implemented' 
>> error.
>> So I thought, we apparently have to implement another method in order 
>> to achieve multiple inheritance:
>>
>> - (struct objc_method_description 
>> *)methodDescriptionForSelector:(SEL)aSelector
>> {
>>    struct objc_method_description    *aDescription = [super 
>> methodDescriptionForSelector:aSelector];
>>    if(aDescription)
>>        return aDescription;
>>
>>    return [[self otherObject] 
>> methodDescriptionForSelector:aSelector];
>> }
>>
>>
>> This then gives the following DO error:
>>
>> 
>> _preInitWithCoder:signature:valid:wireSignature:target:selector:
>> argCount: incompatible method params: got NSMethodSignature: 
>> types=^{objc_method_description=:*}@:: nargs=3 sizeOfParams=160 
>> returnValueLength=4;  want NSMethodSignature: 
>> types=^{objc_method_description=}@:: nargs=3 sizeOfParams=160 
>> returnValueLength=4;
>>

>
> are you using tiger ?


No, but 10.3.9.


> almost all of my DO code gives me the same error on 10.4, it was 
> working like a charm under 10.2 and 10.3
> i think it is a bug in Cocoa DO since 10.4, but i'm not sure...


I think, too.


> i must recognized that i'm lost here...


Me too.


> have you tried a trivial OD test ?


Yes. Trivial method calling works for me. But just not multiple 
inheritance (so far).


Re
Phil