Provides the ruby-1.9 block form of Enumerator, where you can write:

   obj = Enumerator.new do |yielder|
      .. do stuff
      yielder.yield data      # or: yielder << data
      .. etc
   end

When obj.each is called, the block is run once. It should call yielder.yield with each item it wishes to generate.

Example:

  fib = Enumerator.new { |y|
    a = b = 1
    loop {
      y << a
      a, b = b, a + b
    }
  }

  assert_equal [1, 1, 2, 3, 5, 8, 13, 21, 34, 55], fib.take(10)

[Source]

    # File lib/more/facets/enumerator.rb, line 35
35:   def initialize(*args, &block)
36:     if block_given?
37:       @body = block
38:       old_initialize(self, :_start)
39:     else
40:       old_initialize(*args)
41:     end
42:   end