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From: reinhold.may@gmx.de (Reinhold May)
Newsgroups: comp.lang.ada
Subject: Representation Freezing Rules vs. Storage management
Date: 15 Apr 2004 07:36:03 -0700
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Date: 2004-04-15T07:36:03-07:00
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Hi,

I've got a problem with the following code:

   i : integer;
   for i'address use get_address(i'size, i'alignment);

I've compiled an example featuring this  code  using  the  Green
Hills Ada compiler without a problem.

Gnat fails returning:

   representation item appears too late

Although it makes sense to me that this code  compiles  (because
after all knowing the size of a variable and  its  alignment  is
required to find a proper address and thus is probably  required
in  any  kind  of  storage  management),  after   reading   some
contributions to the  newsgroup  and  the  LRM  13.14  (Freezing
Rules), I can understand why Gnat doesn't allow me to do it.

So my first question is, is the above code legal Ada95 code?

If not, does anyone have an idea how I could get the same effect
using legal code?

I thought about using the  type's  attributes  rather  than  the
variable's ones, like the following:

   i : integer;
   for i'address use get_address(integer'size, integer'alignment);

My problem is, I'm having to insert this type of  representation
clause into an existing application (quite a large one).

The application has definitions like:

   a : array(1 .. 10) of integer;

which couldn't be used in a representation clause shown above as
the type is defined implicitely rather than explicitely.  So the
type would have to be defined explicitly on each occurrence.

The type of a variable is not always easy to find out and trying
that would require a full  Ada  parser  (but  of  course  that's
feasible).

A specific 'size respectively 'alignment clause would have to be
recognised and used instead of the type's attributes in order to
get the right address (but with the above mentioned parser  this
would be feasible as well although costing a lot of effort).

Any pointer into the right direction is very welcome.

Thanks,

Reinhold