On Thu, Oct 19, 2006 at 09:56:58AM -0700, Tom Phoenix wrote:
> On 10/19/06, Rob Dixon <[EMAIL PROTECTED]> wrote:
>
> >so the final values of $a and $b are the same regardless and Perl is
> >definitely doing something wrongly in the single-line version.
>
> I would argue that the programmer did something wrongly by abusing the
> auto-increment. But don't let that stop you from filing a bug report,
> if you wish.
>
> If you file a bug report and the response is "Well, don't do that,
> then", don't say you weren't warned. :-)
And that will be the response.
perlop says:
Note that just as in C, Perl doesn't define B<when> the variable is
incremented or decremented. You just know it will be done sometime
before or after the value is returned. This also means that
modifying a variable twice in the same statement will lead to
undefined behaviour. Avoid statements like:
$i = $i ++;
print ++ $i + $i ++;
Perl will not guarantee what the result of the above statements
is.
The key to this is what would be called sequence points and undefined
behaviour in C. Perl doesn't have the formal concepts of sequence
points or undefined behaviour, but in general you should assume it does.
The reasons for the observed behaviour are implementation dependent and
might change in future releases. Once you know what is happening you will
understand why you see the current results (of course), but the behaviour is
not obvious without that understanding.
Reread Lawrence Statton's replies - he knows what he's talking about.
--
Paul Johnson - [EMAIL PROTECTED]
http://www.pjcj.net
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