Interesting experimentation with ruby metaclasses

metaclass_instance_variables.rb

require 'minitest/autorun'

class Monkey
  @@m1 = "monkey"

  class << self
    attr_accessor :m2
  end

  def self.m1=(m)
    @@m1 = m
  end

  def self.m1
    @@m1
  end
end

class Chimp < Monkey
  @@m1 = "chimp"
end

class Spidermonkey < Monkey
  @@m1 = "spidermonkey"
end


class TestTheory < Minitest::Test
  def test_m1_is_at_at_m1
    Monkey.m1 = "m1"
    assert_equal "m1", Monkey.class_variable_get(:@@m1)
  end

  def test_m2_is_not_at_at_m1
    Monkey.m2 = "m2"
    refute_equal "m2", Monkey.class_variable_get(:@@m1)
  end

  def test_m2_is_not_m1
    Monkey.m2 = "m2"
    Monkey.m1 = "m1"
    assert_equal "m2", Monkey.m2
  end

  def test_monkey_m1_is_inherited
    Monkey.m1       = "monkey"
    Spidermonkey.m1 = "spidermonkey"
    Chimp.m1        = "chimp"

    assert_equal "chimp", Monkey.m1
    assert_equal "chimp", Chimp.m1
    assert_equal "chimp", Spidermonkey.m1
  end

  def test_monkey_m2_is_not_inherited
    Monkey.m2       = "monkey"
    Spidermonkey.m2 = "spidermonkey"
    Chimp.m2        = "chimp"

    assert_equal "monkey",       Monkey.m2
    assert_equal "chimp",        Chimp.m2
    assert_equal "spidermonkey", Spidermonkey.m2
  end
end