Difference between Enumerable and Grizzly::Enumerable

list_with_enumerable.rb

class List
  include Enumerable

  attr_reader :items

  def initialize(items)
    @items = items
  end

  def a_thing_to_do
    "calling a_thing_to_do"
  end

  def each
    return to_enum unless block_given?
    items.each { yield _1 }
  end
end

list = List.new([1, 2, 3, 4, 5, 6, 7, 8, 9])

puts list.a_thing_to_do

begin
  list.select(&:even?).a_thing_to_do
rescue NoMethodError => e
  puts e.message
end

new_items = list.select(&:even?)

puts new_items.class
puts List.new(new_items).a_thing_to_do

# calling a_thing_to_do
# undefined method `a_thing_to_do' for [2, 4, 6, 8]:Array

#   list.select(&:even?).a_thing_to_do
#                       ^^^^^^^^^^^^^^
# Array
# calling a_thing_to_do

list_with_grizzly_enumerable.rb

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  gem 'grizzly-rb', require: 'grizzly'
end

class List
  include Grizzly::Enumerable

  attr_reader :items

  def initialize(items)
    @items = items
  end

  def a_thing_to_do
    "calling a_thing_to_do"
  end

  def each
    items.each
  end
end

list = List.new([1, 2, 3, 4, 5, 6, 7, 8, 9])

puts list.a_thing_to_do
puts list.select(&:even?).a_thing_to_do

new_items = list.select(&:even?)

puts new_items.class
puts new_items.a_thing_to_do
puts new_items.select.reject.each(&:odd?).a_thing_to_do

# calling a_thing_to_do
# calling a_thing_to_do
# List
# calling a_thing_to_do
# calling a_thing_to_do