Re: System.Address'Size - not a static integer expression?

[Wes Groleau <wesgroleau@despammed.com>]

> > I found something in the RM that basically insisted that
> > 'Size is non-static.
> 
> Well since you are confused over what static means, I doubt
> this memory is relevant. Once again, while it is true that

Static to me (before Ada 95) meant a value that you can determine
at compile time.  The RM apparently has a different meaning when
it disallowed 
   for xxx'size use ....   (A)
because 'size is not static

The screwed up C definition of static is off in some other planet.

What I was saying was that I tried to use  xxx'size somewhere
that only static values were allowed and it was rejected by both
GNAT and Apex.  At the time, I considered the expression I used
static because it COULD BE determined at compile time.  But
I DID find something in the RM that said 'Size cannot be used
where a static expression is required.

> all static expressions have known-at-compile time values,
> the converse is obviously false (known at compile time values are not
> always static).
> 
> Why? Because it is obviously recursively undecidable whether a given
> expression has a known at compile time
> value (finding all such expressions requires being able
> to prove all possible theorems which of course is not
> possible). So the language had two choices:
> 
>  o Try to pin down a subset of known at compile time
>    expressions and require all compilers to agree on
>    this subset in cases where staticness of expressions
>    has semantic significance (e.g. case tags).

My point exactly:  'Size is not in this subset, no matter
how easy it may be to determine the value.

> So most certainly GNAT and Apex (and any other correct Ada compiler)
> agree on what Size references are static and what
> are not. If the prefix is a static scalar subtype, the size
> reference is static, otherwise it is non-static. End of

So you are saying that it IS in this subset
if the prefix is a static scalar subtype?

First, this is circular, defining static (partially)
in terms that use the word static.

Second, I can no longer remember whether it was a static
scalar subtype, but I do remember (1) the rejection surprised
me after years of Ada experience and (2) the reference _I_
found for (A) above did not have the "static scalar subtype"
exception in it. It just plain said that 'Size is not static.

-- 
Wes Groleau
http://freepages.rootsweb.com/~wgroleau