iter_for.rb

class Iterator < Enumerator
  def initialize obj, meth, *args
    super() do |y|
      loop do
        y << obj
        obj = obj.send(meth, *args)
      end
    end
  end
end

class Object
  def iter_for meth, *args
    Iterator.new self, meth, *args
  end
  alias :to_iter :iter_for
end

method_to_iter.rb

require_relative 'to_iter'

# Note: this conflicts with Object#to_iter
class Method
  def to_iter *args
    Iterator.new receiver, name, *args
  end
end

test_iter_for.rb

require 'test/unit'
require './iter_for.rb'
class IterForTest < Test::Unit::TestCase
  def test_iter_for
    # Test on Integer#next => Integer
    assert_equal([0, 1, 2, 3, 4], 0.iter_for(:next).take(5))
    # Test on String#succ => String
    assert_equal(%w[a b c d e f g h i j], 'a'.iter_for(:succ).take(10))
    # Test on Integer#inspect => String#inspect => String
    assert_equal([1, "1", "\"1\""], 1.iter_for(:inspect).take(3))
  end
  def test_iter_for_args
    # Test with a parameter
    assert_equal([0, 2, 4, 6, 8], 0.iter_for(:+, 2).take(5))
  end
end

test_method_to_iter.rb

require 'test/unit'
require './method_to_iter.rb'
class MethodToIterTest < Test::Unit::TestCase
  def test_to_iter
    # Test on Integer#next => Integer
    assert_equal([0, 1, 2, 3, 4], 0.method(:next).to_iter.take(5))
    # Test on String#succ => String
    assert_equal(%w[a b c d e f g h i j], 'a'.method(:succ).to_iter.take(10))
    # Test on Integer#inspect => String#inspect => String
    assert_equal([1, "1", "\"1\""], 1.method(:inspect).to_iter.take(3))
  end
  def test_iter_for_args
    # Test with a parameter
    assert_equal([0, 2, 4, 6, 8], 0.method(:+).to_iter(2).take(5))
  end
end