Question

I’m traversing an object graph and want to pass it a block that will run on each node of the structure from a method – let’s called visit.

At the top, I’m going to call with a block and I want to delegate the initial call to visit on the root object to visit on other objects. I can unpack the block into a proc locally using &last_parameter_name – but how do I turn the proc back into a block on my delegated call?

Here’s a simplified example where I call first(…) and want to delegate the block through to my call to second(…)

def second(&block)   # ... ? ...
  block.call(72)
end

def first(&block)
  puts block.class     # okay - now I have the Proc version
  puts 'pre-doit'
  block.call(42)
  puts 'post-doit'
  second( ... ? ...)   # how do I pass the block through here?
end

first {|x| puts x*x}

Note: I need to have the same conventions on first() and second() here – i.e. they need to take the same things.

Having read and tried the answers, I’ve come up with a fuller, working example:

class X 
  def visit(&x)
    x.call(50)
  end
end

class Y < X
  def visit(&x)
    x.call(100)
    X.new.visit(&x)
  end
 end

Y.new.visit {|x| puts x*x}

Answer 1

If I understand you correctly, then as simply as

second &block