From: Adam Beneschan <adam@irvine.com>
Subject: Re: Puzzling small piece of code - exception block essentially used as goto
Date: Mon, 04 Jun 2007 17:08:17 -0700
Date: 2007-06-04T17:08:17-07:00 [thread overview]
Message-ID: <1181002097.027416.324060@x35g2000prf.googlegroups.com> (raw)
In-Reply-To: <vQ68i.99$UD4.49@trndny07>
On Jun 1, 10:01 pm, Anonymous Coward <anonym...@coward.org> wrote:
> This is an excerpt from some code I recently encountered (it may give
> some of you a headache):
>
> Still_Looping := True;
>
> Delta_Beyond_Max_Minutes:
> while Still_Looping loop
>
> Handle_Max_Minute_Error:
> begin
>
> Hour_Delta := New_Hour - Hour;
> Still_Looping := False;
> Hour := New_Hour;
>
> exception
> when Constraint_Error =>
>
> if New_Hour > Hour then
>
> Hour_Delta := Max_Hour_Delta
>
> else
>
> Hour_Delta := Relative_Time - Max_Hour_Delta;
>
> end if;
>
> Hour := Hour + Hour_Delta;
>
> end Handle_Max_Minute_Error;
> end loop Delta_Beyond_Max_Minutes;
>
> Tests show that this code actually loops a few times when run in a
> typical state. What I would like clarification on is when the
> exception block ends, where is control returned to?
It goes to the point after the block it's part of, i.e.
Handle_Max_Minute_Error. At that point, it hits the "end loop" and
loops back, if Still_Looping is still true.
It looks like the code is expecting that a Constraint_Error might be
raised on
Hour_Delta := New_Hour - Hour;
Since I don't see the declarations of any of those variables, I don't
know whether it's expecting a Constraint_Error on the subtraction
operation, or on the assignment of the final result to Hour_Delta (if
Hour_Delta is a subrange). But the purpose of the code seems to be
that: if the above subtraction succeeds, we're done; if not, it
adjusts some values and tries again.
> Also, anyone up for the challenge of rewriting this without the
> exception handler so the rest of us humans can understand what it's
> doing?
As noted above, this is really impossible without knowing how those
three key variables are declared.
However, it's possible to write something more readable even with an
exception handler. Here's how I might do it:
Delta_Beyond_Max_Minutes:
loop
begin
Hour_Delta := New_Hour - Hour;
Subtraction_Succeeds := True;
exception
when Constraint_Error =>
Subtraction_Succeeds := False;
end;
if Subtraction_Succeeds then
Hour := New_Hour;
exit;
else
if New_Hour > Hour then
Hour_Delta := Max_Hour_Delta
else
Hour_Delta := Relative_Time - Max_Hour_Delta;
end if;
Hour := Hour + Hour_Delta;
end if;
end loop Delta_Beyond_Max_Minutes;
Is this easier to understand?
(I'm assuming that "Hour := New_Hour;" won't raise an exception.)
-- Adam
next prev parent reply other threads:[~2007-06-05 0:08 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-06-02 5:01 Puzzling small piece of code - exception block essentially used as goto Anonymous Coward
2007-06-02 5:48 ` Jeffrey R. Carter
2007-06-05 2:38 ` Anonymous Coward
2007-06-05 4:10 ` tmoran
2007-06-05 4:53 ` tmoran
2007-06-02 6:16 ` tmoran
2007-06-05 0:08 ` Adam Beneschan [this message]
2007-06-05 7:58 ` anon
2007-06-05 10:40 ` Markus E Leypold
2007-06-05 23:43 ` Anonymous Coward
2007-06-06 10:39 ` Markus E Leypold
2007-06-08 0:55 ` Anonymous Coward
2007-06-08 2:22 ` Markus E Leypold
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