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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: Function Calls by Address
Date: 1999/09/06
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In article <37D41767.CEB186F4@magic.fr>,
  Francois Godme <fgodme@magic.fr> wrote:
> Robert Dewar wrote:
>
> Robert, please can you be less enigmatic. I do not see why it
> is not relevant.
>
> Is it wrong to think that Machine_State_Operations gathered
methods that
> apply on a Machine_State, as its own name may imply? Is it
wrong to
> think that an abstract tagged type could fill the same
purpose, if it
> was allowed in this context?

The point of subunits is to encapsulate locally, whether tagged
types are used or not is an orthogonal issue. Personally I would
find the use of tagged types for this particular purpose to be
a case of clobbering a fly with a sledge hammer, I don't see
that it would add anything. But as I say, the issue is one of
encapsulation. This functionality is strictly local to the
body of ada-exceptions, and subunits capture this relationship
in a natural way.

> By the way, it seems to me that your example only stands as a
> justification for the use of the separate construct in a
language subset
> we don't write programs with, the subset of the Ada language
allowed to
> write the GNAT runtime.

Let me know where you learned of this subset. I have no
awareness of any such restrictions :-)

Certainly we are free to use tagged types if we want to in
the runtime, see for example the way the I/O routines are
programmed and the type File_Type is handled.

Robert Dewar


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