Are there something like Python generators in Ruby?

Question

I am new to Ruby, is there a way to yield values from Ruby functions? If yes, how? If not, what are my options to write lazy code?

Answer 1

Ruby's yield keyword is something very different from the Python keyword with the same name, so don't be confused by it. Ruby's yield keyword is syntactic sugar for calling a block associated with a method.

The closest equivalent is Ruby's Enumerator class. For example, the equivalent of the Python:

def eternal_sequence():   i = 0   while True:     yield i     i += 1 

is this:

def eternal_sequence   Enumerator.new do |enum|     i = 0     while true       enum.yield i # <- Notice that this is the yield method of the enumerator, not the yield keyword       i +=1     end   end end 

You can also create Enumerators for existing enumeration methods with enum_for. For example, ('a'..'z').enum_for(:each_with_index) gives you an enumerator of the lowercase letters along with their place in the alphabet. You get this for free with the standard Enumerable methods like each_with_index in 1.9, so you can just write ('a'..'z').each_with_index to get the enumerator.

Answer 2

I've seen Fibers used in that way, look at an example from this article:

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 }