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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: embed accept statement in procedures not possible?
Date: 4 May 2007 12:45:01 -0700
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Date: 2007-05-04T12:45:01-07:00
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On May 4, 9:58 am, Jean-Pierre Rosen <r...@adalog.fr> wrote:
> Gerd a =E9crit :
>
> > My code (schematic only):
>
> > task t is
> >   entry e;
> > end t;
>
> > task body t is
> >   procedure p is
> >   begin
> >     accept e;
> >   end p;
> > begin
> >   p;
> > end t;
>
> > GNAT tells me: "enclosing body for accept must be a task". But - the
> > accept in procedure p _is_ in a task. So why is this not allowed?
>
> True. An accept statement must be *immediately* within a task body, not
> in anything enclosed in the task body.
>
> That rule is necessary to ensure that a task can accept only its own
> entries. Your example is of course very simple, but consider that a task
> can be included in another task. What if Inner_Task called your P procedu=
re?

Actually, though, why is a syntactic rule necessary (as opposed to a
run-time check)?

Not that I'm proposing a language change.  This is an area I haven't
really given any thought, so I can't say whether the restriction that
prevents "accept" from being done inside a procedure makes life too
burdensome.  But would there be any serious difficulty in changing the
rules so that an "accept" statement is legal inside a procedure, but
raises an exception if the statement is executed under the control of
a task other than the one whose entry is being accepted?  Off the top
of my head (and after about six seconds' worth of thought), I don't
see why this would be unfeasible.

                                         -- Adam