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Postings from March 2008
* Peter Scott <Peter@PSDT.com> [2008-03-28 00:50]:
> At 12:37 PM 3/27/2008, Yitzchak Scott-Thoennes wrote:
>> In point of fact, reusable code which uses scalar-context glob
>> without making sure to exhaust the iterator is buggy. Suppose
>> you have this code instead:
>>
>> sub direxists {
>> print "checking for $_[0]\n";
>> print "$_[0] not found\n" unless glob "/home/?/$_[0]"
>> }
>>
>> Your proposed fix would make it work except in the case of
>> being called with the same parameter twice in a row (where the
>> directory does exist), an even harder problem to debug.
>
> Granted, but I think it is at least easier to defend.
Does ease of defense weigh more important than difficulty of
debugging?
> The current behavior is due to the context argument that is
> supplied by perl and unique per lexical instance. Try
> explaining to someone why this:
>
> print glob("/foo/?") ? "Yes" : "No";
> print glob("/foo/?") ? "Yes" : "No";
>
> produces a different result from this:
>
> for (1..2) {
> print glob("/foo/?") ? "Yes" : "No";
> }
I always thought these operators needed to return an iterator
object instance instead of effectively using the optree as the
namespace for iterator singletons. I assume Perl 6 does that sort
of thing. But that’s not likely to be fixable in Perl 5.
>> I'd rather see a warning for scalar-context glob not in a
>> while() condition, or something like that. (And even that is
>> buggy if the while loop may be prematurely terminated with
>> last or an exception.)
>
> How about this. An analogous situation is scalar m//g, which
> could get you into trouble if you tried hard enough:
>
> my $x = "cba";
> for (qw(a b c))
> {
> print "$x matched /$_/\n" if $x =~ /$_/g;
> }
>
> cba matched /a/
> cba matched /c/
That’s not analogous. The scalar /g iterator is tied to a scalar,
not to a node in the optree. A proper analogy would be the
flip-flop operator. Or `each` in scalar context (but that one
can be reset). All of these are kinda broken as designed.
Regards,
--
Aristotle Pagaltzis // <http://plasmasturm.org/>
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