#!perl

use strict;
use warnings;

BEGIN {
	package Hash::Adjust;
	use Exporter::Shiny 'ha';
	
	sub _generate_ha {
		my ( $me, $name, undef, $opt ) = ( shift, @_ );
		
		my ( $aref, $bref ) = do {
			no strict 'refs';
			my $caller = $opt->{into};
			( \${"$caller\::a"}, \${"$caller\::b"} );
		};
		
		return sub (&\%) {
			my ( $code, $hashref ) = ( @_ );
			@_ = ();
			my %tmp;
			while ( ( $$aref, $$bref ) = each %$hashref ) {
				&$code;
				$tmp{$$aref} = $$bref if defined $$aref;
			}
			%$hashref = %tmp;
		};
	}
};

use Hash::Adjust 'ha';
use Data::Dumper;

my %hash = ( FOO => 42, BAR => 666 );

ha {
	$a =~ s/O/o/g;
	++$b;
} %hash;

print Dumper \%hash;