The anonymous form of sub { ... } is like a dynamic subroutine constructor. Every time you get to the statement

    return sub {$count++}
[download]

the Perl interpreter generates a new sub. It also happens to bundle up any lexical variables that the sub uses, which you seem to understand.

The my $var statement is also like a dynamic variable constructor. Every time you get to a my declaration, a brand new variable is created. Since you construct the closure inside this sub:

sub count_maker {
    my $count = shift;
[download]

So every time you call count_maker, a brand new $count variable is created and bundled up in the brand new anonymous sub closure. Then we leave the scope of count_maker, so that version of $count disappears other than its reference in the anonymous sub that is still around.

There are several things different about your other example. First, the non-anonymous form of sub name { ... } works a little differently. It generates a new sub at compile time, not at runtime when the statement is reached. That's why you can call a named sub that is defined lower down in the file. Also, you have two different $count variables in different scopes. The counter sub is always pointing to the one defined inside the do {} block, not the one in the calling scope. Also, the $count variable that is actually referenced in the sub is never redeclared (the do {} block is never entered more than once).

Here's another example that might be enlightening:

{
  my $count1; ## only one copy of $count1 ever created, so
              ## it's shared by all closures created below

  sub count_maker {
    my $count2 = shift; ## $count2 is a different var each time
                        ## each time we enter count_maker

    return sub { ($count2++, $count1++) }
  }
}

my $c1 = count_maker(1);
my $c2 = count_maker(5);

print join " ", $c1->(), $/;
print join " ", $c2->(), $/;
print join " ", $c2->(), $/;
print join " ", $c1->(), $/;
print join " ", $c1->(), $/;

__OUTPUT__
1 0 
5 1 
6 2 
2 3 
3 4
[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.