From: Matthias Luedtke <matthias-luedtke-usenet@...>
Date: 2005-08-18T07:56:15+09:00
Subject: Passing blocks further down

Hello Rubyists,

at first I must say that after reading this newsgroups for some weeks 
now I'm happy to learn from so many smart and kind people in here. This 
is the place where you actually believe that programming is fun.

I'm implementing a red black tree and I'd like to let users of the class 
be able to traverse it by calling each. I managed to implement the class 
so far but I am unsure whether I use the right technique to pass the 
incoming block from each to the helper method traverse_inorder.

I cut the code down to the minimum, @root is of class Node which looks 
like it's supposed to be :)

class RBTree

   # Visits each node in inorder
   def each(&block)
     traverse_inorder(@root){|x| block.call(x)}
   end

   private
   def traverse_inorder(x, &block)
     if not x.nil? then
       traverse_inorder(x.left){ |n| block.call(n) }
       yield x.key
       traverse_inorder(x.right){ |n| block.call(n) }
     end
   end
end

t = RBTree.new
t.each{ |node| puts node }

Invoking the call method explicitely on the block seems rather odd to 
me. Is it the only way?

Regards,
Matthias