To brighten an otherwise boring day, I decided to teach myself a bit about closures.

The example in the Camel Book (3e, P. 253) worked as advertised:

sub newprint {
    my $x = shift;
    return sub { my $y = shift; print "$x, $y\n"; };
}

$h = newprint("Howdy");
$g = newprint("Greetings");

&$h("world");
&$g("earthlings");
[download]

prints "Howdy, world" and "Greetings, earthlings" just fine. But next I tried:

sub make_closures {
    my $j = 0;
    my @closures;

    while (++$j < 7) {
        push (@closures, sub {print $j, "\n";});
    }
}

foreach my $sub (&make_closures) {
    &$sub;
}
[download]

From the above I got

7
7
7
7
7
7
[download]

from which I conclude, for lack of a better understanding, that the closure gets the value for $j that $j took on when it went out of scope, rather than the value of $j when the closure was defined. If correct, that seems a bit counterintuitive. Can anyone shed some light on this behaviour?

---

---

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.