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NNTP-Posting-Date: Thu, 08 Nov 2012 11:02:00 -0600
From: Chris Hinsley <chris.hinsley@gmail.com>
Newsgroups: comp.lang.forth
Date: Thu, 8 Nov 2012 17:02:00 +0000
Message-ID: <2012110817020085080-chrishinsley@gmailcom>
References: <2012110713421835115-chrishinsley@gmailcom> <2012Nov7.145519@mips.complang.tuwien.ac.at> <2012110715375130718-chrishinsley@gmailcom> <2012Nov8.173134@mips.complang.tuwien.ac.at>
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Subject: Re: Genral advise and comments on callback style words
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On 2012-11-08 16:31:34 +0000, Anton Ertl said:

> Chris Hinsley <chris.hinsley@gmail.com> writes:
>>> However, the may thing I want to point out is that in my experience
>>> it's a good idea if the wrapper word (LISTHEAD-ENUMERATE-FORWARDS in
>>> this case) does not keep its data on the data stack during the
>>> callback, and thus allows the caller to pass additional data to the
>>> called-back word
>> 
>> The u paramater here is exactly that ! A user data value, pointer to
>> structure or whatever. It can be used to pass information to the
>> callback or be used by the callback to pass data onto the next callback
>> invocation etc. It's very flexable.
> 
> It's even more flexible if you avoid any internal data on the data
> stack during the callback, because that allows passing an arbitrary
> number of stack elements into and out of the callback, not just one.
> 
> - anton

Yes, but then surely there will just be similar issues with marshalling 
multiple paramaters on the data stack in the callback and an arguement 
for just passing in a structure pointer and letting the callback 
accsess that structure as required ? It all get's tricky to judge the 
best approach, but I have this API used in other projects in C/C++, so 
kind of like the familiarity of how it works.

Chris