package test;

use strict;
use warnings;

our $self;

sub debug {
  $self->{'debug'}->(@_);
}


sub new {
  my ($class, %params) = @_;
  my $self = { debug => sub {}, %params };
  bless $self, $class;
  return $self;
}

sub method1 {
  local ($self) = @_;
  debug "Entering method1";
}


package main;

use strict;
use warnings;

my $t1 = test->new( debug => sub { print STDERR "debug: @_\n"; } );
my $t2 = test->new( debug => sub { print STDERR "DEBUG: @_\n"; } );

$t1->method1;
$t2->method1;