#!/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";