Re: [Gambas-devel] New(er) enumeration API

[Benoît M. <ga...@us...>]

Le 03/10/2012 20:56, Tobias Boege a écrit :
> On Wed, 03 Oct 2012, Tobias Boege wrote:
>> Hi,
>>
>> today while debugging the new List code for gb.data I encountered problems
>> with the new enumeration API. There are _few_ places to learn from (I took
>> CResult.c) but apparently something doesn't quite work out with it:
>>
>> I want to run through all references I manage for a chunk in a List (a
>> 'chunk' contains some Variants). These are the 'Current' pointer and all the
>> enumerations currently active. The ultimate goal is to update members of
>> these reference structures just because the elements they point to in the
>> chunk changed their location. The convenience macro looks like this:
>>
>> #define for_all_persistent_vals(list, vp, es, ebuf)                     \
>> 	for (ebuf = GB.BeginEnum(list), vp = &list->current, es = NULL;	\
>> 	vp ? 1 : (GB.EndEnum(ebuf), 0);					\
>> 		!GB.NextEnum() ? (es = (struct enum_state*) GB.GetEnum(),\
>> 			vp = &es->next) : (vp = NULL))
>>
>> (admittely not a very appealing piece of code)
>>
>> where 'list' is the Gambas List object, 'vp' is a pointer to the structure
>> I want to update, 'es' is my struct enum_state and 'ebuf' is whatever I get
>> back from GB.BeginEnum() and have to pass to GB.EndEnum().
>>
>> The thing now is that, even if no enumeration runs in the Gambas code, I get
>> some 'es' which contains information that could actually have been valid (in
>> fact, it refers to the last enumerated object in the last enumeration).
>> For some reason, the important part (the pointer to the chunk which sits at
>> offset 0 from the 'es' pointer) is set to NULL and thus, my library
>> segfaults on NULL pointer dereference.
>>
>
> Actually, I set it myself to NULL which indicates the end of enumeration to
> the List_next routine. But why does that 'es' appear again without being in
> enumeration?
>
> I have a really bad feeling now since I only get the 'es' filled if I put in
> some basically unrelated Gambas code before the List.Take() from which the
> above problem originates...
>
> I just want to know: Is it possible under normal circumstances to get an old
> non-running enumerator from that GB.*Enum() interface?
>
>> Benoit, can you please enlighten me if I am doing something wrong with these
>> functions?
>

I can't know. See me the full code because you can't do what you want 
between GB.BeginEnum() ... GB.EndEnum() (i.e. you can't do something 
that may call another enumeration-related function).

Moreover, I'm not sure that your spaghetti macro is right. Can you 
rewrite it as clear as possible (i.e. without using the ',' operator)?

-- 
Benoît Minisini