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Re: objc runtime problem

From: David Ayers
Subject: Re: objc runtime problem
Date: Thu, 26 Jun 2003 19:40:29 +0200
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.4b) Gecko/20030507

Sounds good, but ...

if I read the code in sendmsg.c correctly, you would also have to add the receiver to __objc_get_forward_imp. Then objc_msg_lookup could pass in the receiver. Yet get_imp won't have a means to get the correct fowarding implementation, but that's no worse than before.

Would we only resort to asking the receiver if the supplied selector was untyped, potentially avoiding overhead (potential network traffic... or would that be incurred anyway, i.e use the formal protocol set in the NSDistantObject or do the type syncronisation while determining the forwarding function instead of during it's invokation)

We would be changing the signature of a function (__objc_get_forward_imp) that other code may be using (eventhough they shouldn't (yet it's not like we don't also rely on internal functions)), and more importantly the signature of functions suplied to a public hook would be altered. How would other code be affected if it isn't updated?

Would it be plausible to introduce new variable for forwarding functions with the extra parameter? It would have precedence over the existing one. Maybe we could also have a different name the __objc_get_forward_imp which takes the extra parameter and leave the old implementation... I'm not really sure it's such a good idea but I don't have a feeling for how much this function is used in other projects. The fact that __objc_msg_forward is a public hook of objc-api.h makes me a bit weary.


Richard Frith-Macdonald wrote:

It is currently impossible for these cases to work, because the _objc_msg_forward() function takes a single argument (the selector to look up), but the type information which should be associated with the selector depends on the receiver, and the compiler may have provided an untyped selector, or one with the wrong type info for the receiver.

If sendmsg.c was modified to pass two arguments to the function, (the second being the receiver), the function would be able to ask the receiver for the type information and return a forwarding function which would work for that receiver.

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