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Subject: Re: Joint Strike Fighter
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From: Simon Wright <simon.j.wright@amsjv.com>
Date: 30 Nov 2001 16:26:19 +0000
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Organization: Alenia Marconi Systems, ISD, Farlington
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Ted Dennison<dennison@telepath.com> writes:

> If it took up more than a register I'd say you have a legitimate
> gripe with your compiler vendor. However, you definitely should use
> one of the forms gauranteed to pass by reference if you *need* it
> passed that way for some reason. If you just want it to do the most
> efficient thing (which is the ususal rationale I hear from the C
> refugees), just let the compiler do it.

This was the bug report:

  I have a (private) type Socket:

  type Socket is record
    Fd : Integer;       -- -1 => socket is closed
  end record;

  and a procedure Close:

  procedure Close (The_Socket : in out Socket) is
    Fd : Integer;
  begin
    Fd := The_Socket.Fd;
    The_Socket.Fd := -1;    -- indicate that The_Socket is now closed
    if Close (Fd) < 0 then  -- this is an import of the Unix close()
      raise Close_Error;    
    end if;
  end Close;

  GNAT uses copy semantics here, so if the exception occurs the actual
  parameter doesn't get altered and still has a valid file descriptor,
  leading to confusion downstream.

so making Socket limited would have done as well (I can now see no
reason why I shouldn't have done that .. this was a while back, may
have been a reason at the time). Anyway, it really needed to be by
reference!

-- 
Simon Wright                         Email: simon.j.wright@amsjv.com
Alenia Marconi Systems                     Voice: +44(0)23 9270 1778
Integrated Systems Division                  FAX: +44(0)23 9270 1800