http://www.perlmonks.org?node_id=996029


in reply to Altering the inheritance path of an object

Yes. The basic technique is to create a new package which inherits from the old one but adds some new methods, then rebless the object into that new package. Here's a quick example:

use 5.010; use Math::BigInt; # quite big!! my $seven = Math::BigInt->new('7'); # $seven cannot "speak", so this warns eval { $seven->speak } or warn $@; { package Math::BigInt::Speaker; our @ISA = qw(Math::BigInt); use Scalar::Util qw(blessed); use Carp qw(confess); sub upgrade { my ($class, $instance) = @_; confess "can only upgrade Math::BigInt objects" unless blessed $instance && $instance->isa('Math::BigInt') +; bless $instance => $class; } sub speak { CORE::say($_[0]); } } # Swaps $seven into our new class. Math::BigInt::Speaker->upgrade($seven); # $seven can now "speak" eval { $seven->speak } or warn $@;

If you use Moose you can do this in a much nicer and more organised way. (Though it's basically the same thing happening under the hood.) You'd just create a new anonymous role, and apply that role to the object.

use 5.010; use Math::BigInt; use Moose (); # quite big!! my $seven = Math::BigInt->new('7'); # $seven cannot "speak", so this warns eval { $seven->speak } or warn $@; my $speaker = Moose::Meta::Role->create_anon_role( methods => { speak => sub { CORE::say($_[0]) }, }, ); Moose::Util::apply_all_roles($seven, $speaker); # $seven can now "speak" eval { $seven->speak } or warn $@;
perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'