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Postings from August 2001
John Porter <jdporter@min.net> wrote:
> Dave Mitchell wrote:
> > I think closures are a lot harder (or at least subtler) than people
> > think,
>
> It's hard for me to agree with you, because I've never had *any*
> problems with closures. (And yes, I use them all the time.)
> The scenario you gave seems rather far-fetched to me, in terms
> of real-world programming.
Perhaps, although the following code demonstrates it, and isn't (too)
contrived. Comment out the 'superfluous' "$counters[$i] = 0;" line and
the code stops working. Anyway, I suspect we'll have to agree to disagree :-)
Dave M.
#!./perl
{
my @counters; # private lexicals shared by the 2 subs,
my $index = -1; # but not visible elsewhere
sub new_counter_pair {
$index++;
my $i = $index; # create private snapshot of index
$counters[$i] = 0;
return sub {$counters[$i]++}, sub {$counters[$i]--};
}
sub show_counters {
print join(',', @counters), "\n";
}
}
my ($inc0, $dec0) = new_counter_pair();
my ($inc1, $dec1) = new_counter_pair();
$inc0->();
$inc0->();
$dec0->();
$inc1->();
$inc1->();
show_counters(); # should print "1,2"
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