#!/usr/bin/perl -w
use strict;

# my $x = 1;
tie my $x, 'Tie', 1;
my $f = sub { $x };
print $f->(), "\n"; # => 1
{
    my $scope= tempSet( \$x, 2 );
    print $f->(), "\n"; # => 2
}
print $f->(), "\n"; # => 1

sub TempSet::DESTROY { shift(@_)->() }
sub tempSet {
    my( $sv, $new )= @_;
    my $prior= $$sv;
    my $restore= bless
        sub { $$sv= $prior },
        'TempSet';
    $$sv= $new;
    return $restore;
}

sub Tie::TIESCALAR { return bless \$_[1] => $_[0] }
sub Tie::FETCH { return "${$_[0]} is still tied at line " . (caller())[2] }
sub Tie::STORE { ( ${$_[0]} = $_[1] ) =~ s/ is still tied at line \d+$// }

##</code><code>##

1 is still tied at line 7
2 is still tied at line 10
1 is still tied at line 12