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From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: new revision ada
References: <sa4hdt4o59y.fsf@snoopy.apana.org.au>
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>     tmoran> I don't understand why this is considered a problem.  Why not make:
>     tmoran> type data_to_pass is record ...
>     tmoran> function enstring(x : data_to_pass) return string;
>     tmoran> function destring(s : string) return data_to_pass;
>
> That seems like a very ugly hack.
   Would you prefer something like:
     package ER is new Exception_With_Record(Record_Type => Data_To_Pass);
     Problem : exception;
   ...
   ER.Raise_Exception(Problem'Identity,
                      Data_To_Pass'(Number=>1, RPM=>4000,
                                    Occurred=>After_Switching_Tanks));
   ...
   exception
     when oops:Problem =>
       declare
         Failure_Data : constant Data_To_Pass := ER.Exception_Message(oops);
       ...
The hidden string should contain a pointer to the data to pass, so there's
no problem about 200 character truncation.  It should also contain an
authentication watermark so ER.Exception_Message can avoid trying to
read data from an Ada.Exceptions.Exception_Message string (in case
"raise Problem" was erroneously used instead of ER.Raise_Exception).
ER.Exception_Message would also do the deallocation so the only way
a memory leak could happen is if you don't properly handle the exception,
in which case a memory leak is probably the least of your problems.

> Isn't the philosophy behind Ada that you specify what you want to
> happen, not how it happens?
   I don't understand: all code is a statement of "how it happens",
more or less hidden inside some convenient syntactic form.  Perhaps
Ada.Exceptions.Raise_Exception(Problem'Identity,
                               Enstring(Data_To_Pass'(Number=>1, RPM=>4000,
                                    Occurred=>After_Switching_Tanks)));
is insufficiently opaque.  The above
   ER.Raise_Exception(Problem'Identity,
                      Data_To_Pass'(Number=>1, RPM=>4000,
                                    Occurred=>After_Switching_Tanks));
doesn't expose any internals.

> Thats also a lot of overhead just to pass variables from one part of
> the program to another part of the same program, too.
   I suspect it compares quite well with a call to Ada.Text_IO.Put_Line.
You shouldn't be raising/handling thousands of exceptions/second anyway.