perlquestion
tachyon
<p>I came across an unusual form of closure that I would like someone to explain to me.
You make a regular closere like this:
<code>
{
my $x;
sub foo {
return ++$x;
}
}
for (1..7) { print foo() }
</code>
<p>This prints 1234567 because Perl maintains the $x variable as
sub foo's private memory. OK no suprises there. It's a closure.
<p>Why does this code produce the same effect?
<code>
sub foo {
my $x if undef;
return ++$x;
}
for (1..7) { print foo() }
</code>
<p>It must be a closure but why does Perl
maintain the $x var. If you remove the <tt>if undef</tt> $x behaves
as a lexically scoped var, so as expected we print 1111111 as $x is destroyed and
recreated every time you call the sub. However with this added it
forms a closure so each time we call foo() $x increments and we print 1234567.
A bit of experimentation shows any false value 0, '', or undef elicits this behaviour.
Could someone please explain this?
<p>cheers
<p><font color="#0000ff">tachyon</font>
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