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Postings from July 2010
On Thu, 15 Jul 2010, David Golden wrote:
> I was amusedly thinking that it's not guaranteed to hold true when
> "evaluating" "a" and "b" have magic anyway. (e.g. "a" is tied to
> increment when evaluated and "b" is tied to do something as a function
> of a.
>
> And then we come full circle to the debate that spawned this thread
> about what can be assumed about order of evalution. :-)
My personal opinion is that any FETCH magic or overloaded operator that
has observable side effects is essentially broken and abusing a feature.
You can always use a function or method call if you need exact control
over how your code is being called.
Once you implement magic/overloads that violate the underlying algebraic
relationships in your overloaded operators you will end up in a world
of pain. E.g. the following expressions should always be true:
($a + $b) == ($b + $a)
($a < $b) == ($b <= $a)
"$a" eq $a
($a eq $b) && ($b eq $c) == ($a eq $c)
Perl has different operators for e.g. "==" and "eq", or "+" and "." for
a reason. Don't overload them with semantics that contradicts their
intrinsic behavior!
Once you accept these rules (no side-effects, self-consistent behavior),
the order of evaluation becomes a non-issue.
Perl allows you to shoot yourself in the foot. We should not have to go
out of our way to guarantee that we always hit the same foot...
Cheers,
-Jan
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