Re: [gobo-eiffel-develop] Bug in GEC ?

[Wolfgang J. <wj...@so...>]

Eric Bezault wrote:
> Howard Thomson wrote:
>   
>> Hi Wolfgang and Eric,
>>
>> According to ETL, the '$' operator applied to a non-constant feature should 
>> provide its POINTER address, such that when the pointer is passed to an 
>> external routine, that routine can modify the feature, probably returning a 
>> previously supplied value.
>>
>> Unfortunately, EiffelStudio (I think) does not follow ETL and uses, for a 
>> reference feature, the '$' operator as an equivalent of SmartEiffel's 
>> to_external concept to return the POINTER equivalent of the address of the 
>> referred-to object, which is what Eric has implemented to be compatible with 
>> ES 
>>     
>
> Yes. I think that the idea is that $ does not return the
> address of the attribute entity in the enclosing object,
> but the address of the attribute object. So if the attribute
> is expanded, the address of the object is indeed the same
> as the address of the attribute entity in the enclosing
> object. But for reference attributes, the address of the
> object is what is stored in the attribute entity. So, in
> a sense it is consistent between expanded and reference.
> It's just that it is returning the address of the attribute
> object and not the address of the attribute entity.
>
> I think that ISE gives access to the attribute entity
> address through its class INTERNAL. Because I want to
> implement features of INTERNAL in terms of features of
> class TYPE, I think that I will make this functionality
> available in class TYPE.
>
>   
Hmm, besides the definition of `$' there is another
argument in favour of the address of the entity.
If `$' yields the entity address then
the object address can be obtained via C code
    *(void**)addr
The other way around, obtaining the entity address
from the object address is not possible.
Thus, the entity address carries more information.

The unreferencing might be done by a feature of TYPE,
but how can the reverse operation be accomplished?
I do not know ISE's INTERNAL class very well
but I doubt that there is a function that yields
the entity address of a given reference object:
the best what the function can do is to return
the address of the object (as function argument) on stack.
This is quite meaningless after returning from
the function.

-- 
Wolfgang Jansen
University of Potsdam, Germany
mailto: wj...@so...