Personally, I think it's easiest to think about it in terms of references

In fact, in the following you can see how Perl uses the same reference counting mechanism as for hard references. Hopefully this will now put your mind at ease :-)

#!/usr/bin/env perl
use warnings;
use strict;

# Debugging aids
use Devel::Refcount 'refcount';
use Sub::Delete 'delete_sub';
{
    # This will act like a normal hash except it will print
    # "DESTROY" when it is destroyed (garbage collected).
    package DebugHash;
    BEGIN {
        require Tie::Hash;
        our @ISA = ('Tie::StdHash');
    }
    sub DESTROY { print "DESTROY\n" }
}

{ # Lexical scope for "my %hash".
    
    my %hash; # +1 reference to %hash (0+1=1)
    BEGIN { tie %hash, 'DebugHash' } # tie to debugging aid
    # Note: We'll use $hash{c} as a counter for debug output.
    
    # Apparently BEGIN{} blocks cause +1 reference to %hash (?)
    # Note: refcount()-1 since the argument \%hash is +1 reference.
    BEGIN { print ++$hash{c},": ",refcount(\%hash)-1,"\n" } # "1: 2"
    
    sub foo { # +1 reference to %hash (compile time)
        $hash{x}++;
        print ++$hash{c},": ",refcount(\%hash)-1,"\n";
    }
    BEGIN { print ++$hash{c},": ",refcount(\%hash)-1,"\n" } # "2: 3"
    
    sub bar { # +1 reference to %hash (compile time)
        $hash{y}++;
        my $hashref = \%hash; # +1 reference to %hash (runtime)
        print ++$hash{c},": ",refcount(\%hash)-1,"\n";
    }
    BEGIN { print ++$hash{c},": ",refcount(\%hash)-1,"\n" } # "3: 4"
    
    # Remember "BEGIN" is compile time, the following is run time.
    # The three references to %hash are the lexical "my %hash",
    # as well as "sub foo" and "sub bar".
    print ++$hash{c},": ",refcount(\%hash)-1,"\n";          # "4: 3"
    
} # Lexical scope of "my %hash" ends, -1 reference to %hash.

# The following calls are in "eval" b/c otherwise the calls
# would be another reference keeping &main::foo/bar alive.
eval "foo()";      # "5: 2"
eval "bar()";      # "6: 3"
delete_sub 'bar';  # -1 reference to %hash
eval "foo()";      # "7: 1"
delete_sub 'foo';  # -1 reference to %hash (1-1=0) => "DESTROY"

print "Done.\n";
[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.