•Re: Change the parent of an instance

[merlyn]

Well, you could do this by re-blessing, but that'll suck. Instead, you should have a member variable that handles certain behaviors as a pluggable value, and then replace that member variable as the role of the object changes.

[muba]

What's wrong with reblessing then? The variable keeping track of the actual type might be a good idea, but many of the methods will then look like

if ($somehow_is_a_foe) {
} else {
}

because the two share a lot, although they hardly share anything.

Update: I have not yet thought about re-blessing. I think it's a good idea, worthwhile trying but if you say it's bad (or at least, will suck) I'll be glad to know why, just to find out if re-blessing is what I want.

[merlyn]

No, I mean you plug it like this:

package Elf;
sub named {
  my $class = shift;
  bless {
    Name => shift;
    Actions => Elf::Live::,
    Has => {},
  }, $class;
}

sub die {
  shift->{Actions} = Elf::Dead::;
}

sub can_attack { # delegate to actions
  shift->{Actions}->can_attack(@_);
}

sub enemy_of {
  shift->{Actions}->enemy_of(@_);
}

package Elf::Live;

sub can_attack { ... }

sub enemy_of { ... }

package Elf::Dead;

sub can_attack { ... }

sub enemy_of { ... }

A simple change of the Actions variable by plugging in a different "behavior container" causes a bank-switch of those behaviors to a new motif. I forget the "gang of four" pattern for this, but it's one of those. {grin}

[Fletch]

See also the "Gang of Four" book (ISBN 0201633612) for Strategy and State.

[muba]

Ah! Now I see!

I think it's the best idea I've seen so far, assuming re-blessing really sucks. I'll have a look at it (a big re-style of the code is now required but it's worth it).

Just for my information, could you please tell me the disadvanteges of re-blessing?