src/about_class_methods.rb

   1 require File.expand_path(File.dirname(__FILE__) + '/edgecase')
   2
   3 class AboutClassMethods < EdgeCase::Koan
   4   class Dog
   5   end
   6
   7   def test_objects_are_objects
   8     fido = Dog.new
   9     assert_equal __(true), fido.is_a?(Object)
  10   end
  11
  12   def test_classes_are_classes
  13     assert_equal __(true), Dog.is_a?(Class)
  14   end
  15
  16   def test_classes_are_objects_too
  17     assert_equal __(true), Dog.is_a?(Object)
  18   end
  19
  20   def test_objects_have_methods
  21     fido = Dog.new
  22     assert fido.methods.size > _n_(30)
  23   end
  24
  25   def test_classes_have_methods
  26     assert Dog.methods.size > _n_(40)
  27   end
  28
  29   def test_you_can_define_methods_on_individual_objects
  30     fido = Dog.new
  31     def fido.wag
  32       :fidos_wag
  33     end
  34     assert_equal __(:fidos_wag), fido.wag
  35   end
  36
  37   def test_other_objects_are_not_affected_by_these_singleton_methods
  38     fido = Dog.new
  39     rover = Dog.new
  40     def fido.wag
  41       :fidos_wag
  42     end
  43
  44     assert_raise(___(NoMethodError)) do
  45       rover.wag
  46     end
  47   end
  48
  49   # ------------------------------------------------------------------
  50
  51   class Dog2
  52     def wag
  53       :instance_level_wag
  54     end
  55   end
  56
  57   def Dog2.wag
  58     :class_level_wag
  59   end
  60
  61   def test_since_classes_are_objects_you_can_define_singleton_methods_on_them_too
  62     assert_equal __(:class_level_wag), Dog2.wag
  63   end
  64
  65   def test_class_methods_are_independent_of_instance_methods
  66     fido = Dog2.new
  67     assert_equal __(:instance_level_wag), fido.wag
  68     assert_equal __(:class_level_wag), Dog2.wag
  69   end
  70
  71   # ------------------------------------------------------------------
  72
  73   class Dog
  74     attr_accessor :name
  75   end
  76
  77   def Dog.name
  78     @name
  79   end
  80
  81   def test_classes_and_instances_do_not_share_instance_variables
  82     fido = Dog.new
  83     fido.name = "Fido"
  84     assert_equal __("Fido"), fido.name
  85     assert_equal __(nil), Dog.name
  86   end
  87
  88   # ------------------------------------------------------------------
  89
  90   class Dog
  91     def Dog.a_class_method
  92       :dogs_class_method
  93     end
  94   end
  95
  96   def test_you_can_define_class_methods_inside_the_class
  97     assert_equal __(:dogs_class_method), Dog.a_class_method
  98   end
  99
 100
 101   # ------------------------------------------------------------------
 102
 103   LastExpressionInClassStatement = class Dog
 104                                      21
 105                                    end
 106
 107   def test_class_statements_return_the_value_of_their_last_expression
 108     assert_equal __(21), LastExpressionInClassStatement
 109   end
 110
 111   # ------------------------------------------------------------------
 112
 113   SelfInsideOfClassStatement = class Dog
 114                                  self
 115                                end
 116
 117   def test_self_while_inside_class_is_class_object_not_instance
 118     assert_equal __(true), Dog == SelfInsideOfClassStatement
 119   end
 120
 121   # ------------------------------------------------------------------
 122
 123   class Dog
 124     def self.class_method2
 125       :another_way_to_write_class_methods
 126     end
 127   end
 128
 129   def test_you_can_use_self_instead_of_an_explicit_reference_to_dog
 130     assert_equal __(:another_way_to_write_class_methods), Dog.class_method2
 131   end
 132
 133   # ------------------------------------------------------------------
 134
 135   class Dog
 136     class << self
 137       def another_class_method
 138         :still_another_way
 139       end
 140     end
 141   end
 142
 143   def test_heres_still_another_way_to_write_class_methods
 144     assert_equal __(:still_another_way), Dog.another_class_method
 145   end
 146
 147   # THINK ABOUT IT:
 148   #
 149   # The two major ways to write class methods are:
 150   #   class Demo
 151   #     def self.method
 152   #     end
 153   #
 154   #     class << self
 155   #       def class_methods
 156   #       end
 157   #     end
 158   #   end
 159   #
 160   # Which do you prefer and why?
 161   # Are there times you might prefer one over the other?
 162
 163   # ------------------------------------------------------------------
 164
 165   def test_heres_an_easy_way_to_call_class_methods_from_instance_methods
 166     fido = Dog.new
 167     assert_equal __(:still_another_way), fido.class.another_class_method
 168   end
 169
 170 end