gistfile1.pl

    use Data::Delay;
    
    my $test = 1;
    my $data = Data::Delay->new(\$test);
    
    print $data; # 1
    $test = 2;
    print $test; # 2
    
    my $plus = Data::Delay->New(sub { $data + 2 });
    print $plus; # 4
    
    $test = -2;
    print $plus; # 0