I have a class, and I want to be able supply it with a debug sub for printing debug messages, on a per-object basis.

My first implementation looks something like this:

package test;

use strict;
use warnings;

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

sub method1 {
  my ($self) = @_;
  $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;

[download]

This works fine, but I'm rather lazy and would prefer to avoid the long $self->{'debug'}->("text") invocation for each debug message. I'd prefer to be able to just say debug("text") and have it DWIM.

So I changed the code to this:

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;

[download]

Which seems to do the trick.

So now I have two questions:

  1. What are the downsides to doing it this way? One obvious issue is that the passed subroutine can now access and modify $self. I suspect there may be some issues once inheritance comes into play, but I haven't done any testing on that yet.
  2. Is there a better way to do this? (or should I just forget about the whole thing and use the long invocation)

In reply to Short invocation for per-object methods by Crackers2

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