koans/about_constants.rb

   1 require File.expand_path(File.dirname(__FILE__) + '/edgecase')
   2
   3 C = "top level"
   4
   5 class AboutConstants < EdgeCase::Koan
   6
   7   C = "nested"
   8
   9   def test_nested_constants_may_also_be_referenced_with_relative_paths
  10     assert_equal __, C
  11   end
  12
  13   def test_top_level_constants_are_referenced_by_double_colons
  14     assert_equal __, ::C
  15   end
  16
  17   def test_nested_constants_are_referenced_by_their_complete_path
  18     assert_equal __, AboutConstants::C
  19     assert_equal __, ::AboutConstants::C
  20   end
  21
  22   # ------------------------------------------------------------------
  23
  24   class Animal
  25     LEGS = 4
  26     def legs_in_animal
  27       LEGS
  28     end
  29
  30     class NestedAnimal
  31       def legs_in_nested_animal
  32         LEGS
  33       end
  34     end
  35   end
  36
  37   def test_nested_classes_inherit_constants_from_enclosing_classes
  38     assert_equal __, Animal::NestedAnimal.new.legs_in_nested_animal
  39   end
  40
  41   # ------------------------------------------------------------------
  42
  43   class Reptile < Animal
  44     def legs_in_reptile
  45       LEGS
  46     end
  47   end
  48
  49   def test_subclasses_inherit_constants_from_parent_classes
  50     assert_equal __, Reptile.new.legs_in_reptile
  51   end
  52
  53   # ------------------------------------------------------------------
  54
  55   class MyAnimals
  56     LEGS = 2
  57
  58     class Bird < Animal
  59       def legs_in_bird
  60         LEGS
  61       end
  62     end
  63   end
  64
  65   def test_who_wins_with_both_nested_and_inherited_constants
  66     assert_equal __, MyAnimals::Bird.new.legs_in_bird
  67   end
  68
  69   # QUESTION: Which has precedence: The constant in the lexical scope,
  70   # or the constant from the inheritance hierarchy?
  71
  72   # ------------------------------------------------------------------
  73
  74   class MyAnimals::Oyster < Animal
  75     def legs_in_oyster
  76       LEGS
  77     end
  78   end
  79
  80   def test_who_wins_with_explicit_scoping_on_class_definition
  81     assert_equal __, MyAnimals::Oyster.new.legs_in_oyster
  82   end
  83
  84   # QUESTION: Now which has precedence: The constant in the lexical
  85   # scope, or the constant from the inheritance hierarchy?  Why is it
  86   # different than the previous answer?
  87 end