lazy evaluation - 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?

question from:https://stackoverflow.com/questions/2504494/are-there-something-like-python-generators-in-ruby

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.