[MOAB-dev] Incomplete types versus void * in ITAPS interfaces

[Carl Ollivier-Gooch]

Tim Tautges wrote:
> Interesting question, which I'm forwarding to the rest of the ITAPS 
> interface group.  One question, would that require you to actually 
> define the private structure, or just reference it?  The extra type 
> checking would be very useful (and would be useful inside MOAB as well...).

My first reaction was that I never would have thought that this would be 
compilable.  Jed obviously knows something about C syntax that I don't, 
because it does seem to work, at least in terms of compiling and linking 
(see attached files).  I defined two different structs, one in C, one in 
C++, and both linked fine (as in: both test2.o and test3.o link with 
test.o with no complaints).  Mind you, I never tried to do anything 
beyond what's in these files, so it's possible that the compiler 
optimized away anything that might have been a problem.

 From the implementation side, if we made this change, we'd all have to 
have an explicit iBase_EntityHandle_Private (plus half a dozen or so 
others), but in exchange we get type checking and may be able to avoid a 
bunch of casts (that's probably implementation dependent...

Carl

> Jed Brown wrote:
>> Sorry if this is the wrong list for this, but why are all the opaque
>> handles typedef'd to void * instead of incomplete types.  That is, why
>> not something like
>>
>>   typedef struct iBase_EntityHandle_Private *iBase_EntityHandle;
>>
>> in order to get some extra type checking?  Correct existing code should
>> not see any difference.  With this change, a possible logic error (using
>> EntitySetHandle for an EntitySet) in the VisIt plugin would be caught by
>> the compiler.
>>
>> Jed
> 


-- 
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Dr. Carl Ollivier-Gooch, P.Eng.                   Voice: +1-604-822-1854
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