#!/usr/bin/perl
use strict;
use warnings;

use Tk;


package Test;
sub new {
    my $class = shift;
    my $self  = {
        counter => 0,
    };

    bless $self, ref($class)||$class;

    return $self;
}

sub add_to_counter {
    my ( $self, $value, ) = @_;

    $self->{counter} += $value       if $value;

    return \$self->{counter};
}


package main;


my $counter = 0;

my $test = Test->new();

my $mw = tkinit();

my $button1 = $mw->Button(-textvariable => \$counter)->pack();
my $button2 = $mw->Button(-textvariable => $test->add_to_counter()  )->pack();

$mw->repeat(100 => sub { fetch_data($test) });
MainLoop;

sub fetch_data {
  my $obj = shift;

  $counter++;
  $obj->add_to_counter( 1 );
}


1;