I see haj made the same suggestion as I was working on the following code: you can use tie to tie a scalar to a class, where you can customize the "fetch" and "store" events. See also perltie and Tie::Scalar. I tried this with your sample code and it works there as well.

use warnings;
use strict;

{
    package Tie::Scalar::Callbacks;
    sub TIESCALAR {
        my $class = shift;
        my %self;
        @self{qw/ val store_cb fetch_cb /} = @_;
        return bless \%self, $class;
    }
    sub FETCH {
        my $self = shift;
        $self->{fetch_cb}->($self->{val}) if $self->{fetch_cb};
        return $self->{val};
    }
    sub STORE {
        my $self = shift;
        my $val = shift;
        $self->{store_cb}->($self->{val}, $val) if $self->{store_cb};
        $self->{val} = $val;
    };
    sub DESTROY { %{shift()}=() }
}

tie my $name, 'Tie::Scalar::Callbacks', "foo",
    sub { print "storing <$_[1]>, was <$_[0]>\n" };
print "name is $name\n";
$name = "bar";
print "name is $name\n";

__END__

name is foo
storing <bar>, was <foo>
name is bar

[download]

Minor update to constructor.

In reply to Re: call subroutine if scalar is changed by haukex
in thread call subroutine if scalar is changed by Anonymous Monk

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