Re: Potential Coextension Bug in GNAT

[Jere <jhb.chat@gmail.com>]

On Thursday, December 20, 2018 at 9:25:42 PM UTC-5, Randy Brukardt wrote:
> <SNIPPED> 
> 
> So it does look like a GNAT bug. There is the possibility that they are 
> associating the discriminant with the temporary object associated with the 
> allocator, and not the return object, but that seems unnecessarily 
> unfriendly of an interpretation. And it would be wrong for any type that 
> requires built-in-place (I didn't look at the actual declaration of the 
> type). I think the rules are supposed to prevent that interpretation, but 
> whether they really do is an interesting question that I have no interest in 
> exploring.
Ok, that makes me feel better.  I was concerned I was misinterpreting the
RM about the function return (for build in place).  The type was limited, 
which I believe requires it to be build in place.


> 
> P.S. Did I mention I hate coextensions?? They provide an endless opportunity 
> to puzzle over rules that really don't matter in the end (and most likely 
> aren't quite right). I suppose they've helped me keep employed running the 
> ARG. :-)

Overall, they aren't super useful and are not very intuitive.  I don't know
the history for why they were added to the language though.  I will say
they do provide one thing to Ada that no other feature in the language 
seems to, so there is that.  But I don't know the cost versus reward of them.