This is related to the hack used to implement state variables in subroutines, before state variables have been implemented in perl 5.10.0, which emits a warning on recent perls. It allocates the lexical variable on the subroutine's pad (or better: the pad of the current scope), but prevents it from being cleared:

#file state.pl
sub foo {
    my $bar if 0;
    $bar++;
    print "foo called $bar times\n";
}
foo for 'a'..'f';
__END__
Deprecated use of my() in false conditional at state.pl line 2.
foo called 1 times
foo called 2 times
foo called 3 times
foo called 4 times
foo called 5 times
foo called 6 times
[download]

This works also for lexical arrays.

However, if the conditional is declared beforehand as a variable, there is no such warning, since that warning happens at compile time, but the conditional is resolved at runtime:

# file state.pl
my $cond;
sub foo {
    my @bar if $cond;
    push @bar, @_;
    print "array \@bar = (@bar)\n";
}
foo $_ for 'a'..'f';
$cond = 1;
foo $_ for 1..6;
__END__
array @bar = (a)
array @bar = (a b)
array @bar = (a b c)
array @bar = (a b c d)
array @bar = (a b c d e)
array @bar = (a b c d e f)
array @bar = (a b c d e f 1)
array @bar = (2)
array @bar = (3)
array @bar = (4)
array @bar = (5)
array @bar = (6)
[download]

Huh? We have array @bar = (a b c d e f 1) here? Well, my variables are cleared at the end of their scope, so setting $cond = 1 doesn't clear the (state) array immediately.

If you don't have a sophisticated use (read: obfuscated use) for altering the behavior of my variables, you should use:

use feature qw(state);
# also
use 5.10.0;

sub foo {
    state @bar;
    ...
}
[download]

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.