Re: on the fly methods

[Fletch]

This is Perl, not Ruby. Methods are subs in a given package, not properties of individual instances. You possibly could do some dark magic with AUTOLOAD (make it lookup say $self->{_instancemethods}->{$AUTOLOAD} and call that if it exists), or eval new code into the instance's package (eval qq{ package @{[ ref $self ]}; sub { "NEW CODE" }}; however that's going to make the method available on all instances of that class (and its descendants) not just the one in $self)).

Perhaps you could elaborate on what you're trying to do and you might get better suggestions (e.g. yes, you're trying to emulate Ruby's

class << obj
  def new_method
   "fweeee"
  end
end

in order to add a method on a single instance).

Update: Formatting and wording tweaks.

[diotalevi]

If you use any of Class::Trait, Class::MOP, or Moose then objects can have their own methods. (I'm guessing that Moose does this because it uses MOP which provides this service).

[stvn]

Actually Class::MOP does not provide for a (direct) way to add methods to an instance, it mostly deals with just classes. And with Moose, there is no way to add a single method on a per-instance basis really either, you do it with runtime Roles instead, like this:

{
    package My::Class;
    use Moose;

    sub hello { "Hello" }

    package My::Role;
    use Moose::Role;

    sub foo { "Foo" }
}

my $obj_1 = My::Class->new;
my $obj_2 = My::Class->new;

My::Role->meta->apply($obj_1);

print $obj_1->foo; # print "Foo"
print $obj_2->foo; # dies with a method not found error

Also Class::Trait does this same type of thing using Traits instead of Roles.

Ruby accomplishes this type of thing with "Eigenclasses" which were in the Perl 6 metamodel at one time, but were not backported to Moose (because they tended to make simple metaclass things overly complex). The Ruby idiom of:

class << obj
  def new_method
   "fweeee"
  end
end

roughly translates into this:

obj.add_singleton_method(lambda { "fweee" })

where add_singleton_method is just a method in Object. Something like this could be added to Moose without too much trouble at all really (no AUTOLOAD tricks needed either).

[friedo]

Also Class::Unique. I'm a big fan for some reason. :)

[jettero]

I had never heard of Moose before this, but I think it's potentially something I could one day use in all my new OO code. Wow, just wow.

[diotalevi]

I think Moose is a port of Perl 6's OO system back to Perl 5.