From: dave.burt@...
Date: 2005-08-12T12:41:11+09:00
Subject: Re: Head First Design Patterns - Strategy Pattern [was: Java/C# "interface" in Ruby ?]

> Although Peter's demo didn't illustrate it, the key to the strategy pattern is
> that the strategy can be dynamically chosen (and changed) at runtime.

While the solution I gave is able to do that, thanks to Ruby's ease of
reflection, if that's the case, maybe you do want to use delegation
like I did above.

If a Strategy is a single function, I'd probably do it more like this,
though:

Quack = proc do
  puts "Quack!"
end

DaffyQuack = proc do
  puts "Consequences, schmonsequences, as long as I'm rich!"
end

Class Duck
  def initialize() @quacker = Quack end
  def quack(*args, &block) @quacker.call(*args, &block) end
  def attr_writer :quacker
end

daffy = Duck.new
daffy.quack  #=> "Quack"
daffy.quacker = DaffyQuack
daffy.quack #=> "Consequences, schmonsequences, as long as I'm rich!"

For multi-function/method strategies, you might consider using
Forwardable to delegate specific methods to modules or objects in
instance variables.

Cheers,
Dave