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From: lee@leo (Bill Lee)
Newsgroups: comp.lang.ada
Subject: Re: Updating IN OUT's after exceptions
Message-ID: <1991May3.125143.3704@shell.shell.com>
Date: 3 May 91 12:51:43 GMT
References: <33747@mimsy.umd.edu> <20600103@inmet>
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Organization: Shell Oil
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In article <20600103@inmet> stt@inmet.inmet.com writes:
>
>Re:  Updating IN OUT's after exceptions 
>         Query on  5:18 am  Apr 30, 1991 by stuartw@tove.cs.umd.edu
>
>> In the enclosed program, I raise an exception inside a subroutine after
>> making an assignment to an IN OUT parameter.  In the first case, the
>> parameter is a scalar, in the second it is not.  Everything else is the
>> same, except the resulting behavior.  Is this permitted by the LRM?
>> I know that compilers can pass non-scalar parameters by copy-in/copy-out
>> or reference, but should that effect exception handling?  Is Ada/9x
>> addressing this?
>> 
>> Thanks.
>> 
>> Stuart.  (weinstei@kong.gsfc.nasa.gov)
>
>The Good Old Reference Manual, section 6.2:12 says the following:
>  If the execution of a subprogram is abandoned as a result of an exception,
>  the final value of an actual parameter [...] can be either its
>  value before the call [if passed by copy] or a value assigned
>  to the formal parameter during the execution of the subprogram
>  [if passed by reference].
>
>In other words, the compiler "does the right thing."
>
>S. Tucker Taft
>Intermetrics, Inc.
>Cambridge, MA  02138


The "Right Thing"??? Yes,.....but.....

THERE ARE NO GUARANTEES THAT ANY TWO COMPILERS WILL DO IT THE SAME!

Any program that depends on a particular implementation of the values
returned (or not returned) in a record or array under the conditions
specified is technically erroneous. Sure, it will work on the first
compiler/platform, but there is no way to believe that it will work
elsewhere.

Bill Lee			lee@shell.com
Shell Oil Co.