From: Gregory Millam <walker@...>
Date: 2004-02-27T02:49:56+09:00
Subject: Re: Callback

Received: Fri, 27 Feb 2004 02:29:48 +0900
And lo Han wrote:

> class A
>   def callback(name, obj)
>     @obj = obj
>     eval("def #{name}; @obj.keys; end")
>   end 
> end
> 
> class B
>   attr_reader :keys
>   def initialize(k, cb)
>     @keys = k
>     cb.callback('cassette', self)
>   end
> end
> 
> a = A.new
> g = B.new([1,2,3], a)
> puts a.cassette
> 

class A
  def initialize
    @cb_hash = Hash.new(nil)
  end
  def callback(name,&block)
    @cb_hash[name.to_sym] = block if block_given?
  end
  def method_missing(name,*args)
    return @cb_hash[name].call(*args) if @cb_hash.has_key?(name)
  end
end

a = A.new
a.callback("mykeys") {
  [1,2,3]
}

puts a.mykeys.join(', ') #=> 1, 2, 3

class B
  def initialize(k,cb)
    cb.callback("cassette") { k }
  end
end

b = B.new([4,5,6],a)

puts a.cassette.join(', ') #=> 4, 5, 6

Personally, I think writing a caller in class A (i.e a.call("cassette").join) instead of method missing makes more sense, but it's up to you.

Options left to the reader: allow 'callback' to accept blocks and non-blocks, and have method_missing (or call()) act differently depending on if it's a proc block or not: i.e returning the value instead of calling it.

I hope this helped,

- Greg