Re: The Incredible Shrinking Type

["Marc A. Criley" <mcquad@earthlink.net>]

Robert Dewar wrote:
> 
> In article <3A0703F5.9333AE56@earthlink.net>,
>   "Marc A. Criley" <marccriley@earthlink.net> wrote:
> 
> > However, when passing an instance of this type as a parameter
> to a procedure and
> > extracting its 'Size, the result is 64.  What happened to the
> rest of the bits?
> > Granted, they were unused, but still...  Where is this
> behavior addressed by the
> > language (if it is), or is it a freedom granted to compiler
> implementor's?
> 
> You are making the common mistake of confusing the size of
> a type with the size of objects of the type. Specifying the
> size of a type only affects packing and unchecked conversion
> in Ada 95 semantics. It does not determine the size of
> objects of the type, and there is no requirement that the
> size of all objects of the type be the same.

Actually I do understand the distinction between the sizes of a type and
objects of that type. That's been very well beaten into me over the last
couple years.  In my case, I guess there's still been a residual
reluctance to accept that specifying the size of a type only affects
packing and Unchecked_Conversion. Especially since compilers do usually
try to utilize that size (in some way, as demonstrated in the example)
when allocating objects of that type--implying there is a semantic
effect beyond those two areas.

However, today, the last of the residual reluctance has finally been
cleared away...and I do believe! :-)

> 
> So the real issue here is what you have read in the RM that
> implies that the above behavior is expected or not expected.
> Actually asking for more than 64 bits for a scalar type is
> a bit peculiar anyway (and way out of the portable behavior
> required by the RM).
> 

I agree this is a peculiar use.  Fortunately I'm not employing that
technique, I just want to be able to properly and accurately analyze any
such peculiar software that I may come across.

Marc A. Criley
Senior Staff Engineer
Quadrus Corporation