In my experience, monkey patching usually is not worth its trouble. The problem you describe above I would solve by subclassing + duck typing: in Example::ErrorList, provide a method that returns list item class name, and instantiate objects of that name. This way you can subclass both Example::ErrorList and Example::Error in a "clean" way.
Like this:
package Example::ErrorList;
sub list_item_class { 'Example::Error' }
sub new {
my ($class) = @_;
my $item_class = $class->list_item_class;
my $self = bless {}, $class;
$self->{items} = [ map { $item_class->new($_) } @seed_list_or_some
+thing ];
return $self;
}
package Example::Error;
sub as_string {
die "as_string should be implemented by subclass";
}
sub asplode {
my ($self) = @_;
die "BANG! ".$self->as_string;
}
package My::AwesomeErrorList;
use base 'Example::ErrorList';
sub list_item_class { 'My::AwesomeError' }
package My::AwesomeError;
use base 'Example::Error';
sub as_string {
# Actually implement it
}
You also have a typo: my $self = @_; won't work the way you expect.
Regards,
Alex.