Fibonacci numbers with Ruby 1.9 Fibers

Here's how to use the new Fiber class (warning: class name may change) to generate an infinite sequence of Fibonacci numbers. I use "generate" in the sense of Python's generators. Ruby's new fibers are "semi-coroutines"

fib = Fiber.new do 
  x, y = 0, 1
  loop do 
    Fiber.yield y
    x,y = y,x+y
  end
end

20.times { puts fib.resume }

Remember that the Fiber class was added to Ruby 1.9 yesterday, so you need a very recent snapshot to make this work.

Here's a slightly higher-level way to do the Fibonacci numbers. We hide the Fiber class inside of a Generator class:

class Generator
  def initialize &block
    @f = Fiber.new &block
  end

  def next?
    @f.alive?
  end

  def next(*args)
    @f.resume(*args)
  end
end

fib2 = Generator.new do 
  x, y = 0, 1
  loop do 
    Fiber.yield y
    x,y = y,x+y
  end
end
20.times { puts fib2.next }