http://qs1969.pair.com?node_id=573959


in reply to Re^2: adding temporary method to a class
in thread adding temporary method to a class

This sounds like something for which code references would be more suitable.

After reading up on the Visitor pattern — I wasn't familiar with it by name — I dare say it *is* something for which code references would be more suitable. The example on that paged could be implemented as follows in Perl:

use strict; use warnings; { package Wheel; sub new { my ($class, $name) = @_; return bless({ name => $name }, $class); } sub get_name { my ($self) = @_; return $self->{name}; } sub accept { my ($self, $visitor) = @_; $visitor->($self); } } { package Engine; sub new { my ($class) = @_; return bless({}, $class); } sub accept { my ($self, $visitor) = @_; $visitor->($self); } } { package Body; sub new { my ($class) = @_; return bless({}, $class); } sub accept { my ($self, $visitor) = @_; $visitor->($self); } } { package Car; sub new { my ($class) = @_; return bless({ engine => Engine->new(), body => Body->new(), wheels => [ map { Wheel->new($_) } 'front left', 'front right', 'back left', 'back right', ], }, $class); } sub accept { my ($self, $visitor) = @_; $visitor->($self); $self->{engine}->accept($visitor); $self->{body}->accept($visitor); $_->accept($visitor) foreach @{$self->{wheels}}; } } sub visitor { my ($o) = @_; if ($o->isa('Wheel')) { print("Visiting ", $o->get_name(), " wheel\n"); } elsif ($o->isa('Body')) { print("Visiting body\n"); } elsif ($o->isa('Engine')) { print("Visiting engine\n"); } elsif ($o->isa('Car')) { print("Visiting car\n"); } else { die("Unknown class " . ref($o)); } } { my $car = Car->new(); $car->accept(\&visitor); }