koans/about_symbols.rb

   1 require File.expand_path(File.dirname(__FILE__) + '/edgecase')
   2
   3 class AboutSymbols < EdgeCase::Koan
   4   def test_symbols_are_symbols
   5     symbol = :ruby
   6     assert_equal __, symbol.is_a?(Symbol)
   7   end
   8
   9   def test_symbols_can_be_compared
  10     symbol1 = :a_symbol
  11     symbol2 = :a_symbol
  12     symbol3 = :something_else
  13
  14     assert_equal __, symbol1 == symbol2
  15     assert_equal __, symbol1 == symbol3
  16   end
  17
  18   def test_identical_symbols_are_a_single_internal_object
  19     symbol1 = :a_symbol
  20     symbol2 = :a_symbol
  21
  22     assert_equal __, symbol1           == symbol2
  23     assert_equal __, symbol1.object_id == symbol2.object_id
  24   end
  25
  26   def test_method_names_become_symbols
  27     symbols_as_strings = Symbol.all_symbols.map { |x| x.to_s }
  28     assert_equal __, symbols_as_strings.include?("test_method_names_become_symbols")
  29   end
  30
  31   # THINK ABOUT IT:
  32   #
  33   # Why do we convert the list of symbols to strings and then compare
  34   # against the string value rather than against symbols?
  35
  36   in_ruby_version("mri") do
  37     RubyConstant = "What is the sound of one hand clapping?"
  38     def test_constants_become_symbols
  39       all_symbols = Symbol.all_symbols
  40
  41       assert_equal __, all_symbols.include?(__)
  42     end
  43   end
  44
  45   def test_symbols_can_be_made_from_strings
  46     string = "catsAndDogs"
  47     assert_equal __, string.to_sym
  48   end
  49
  50   def test_symbols_with_spaces_can_be_built
  51     symbol = :"cats and dogs"
  52
  53     assert_equal symbol, __.to_sym
  54   end
  55
  56   def test_symbols_with_interpolation_can_be_built
  57     value = "and"
  58     symbol = :"cats #{value} dogs"
  59
  60     assert_equal symbol, __.to_sym
  61   end
  62
  63   def test_to_s_is_called_on_interpolated_symbols
  64     symbol = :cats
  65     string = "It is raining #{symbol} and dogs."
  66
  67     assert_equal __, string
  68   end
  69
  70   def test_symbols_are_not_strings
  71     symbol = :ruby
  72     assert_equal __, symbol.is_a?(String)
  73     assert_equal __, symbol.eql?("ruby")
  74   end
  75
  76   def test_symbols_do_not_have_string_methods
  77     symbol = :not_a_string
  78     assert_equal __, symbol.respond_to?(:each_char)
  79     assert_equal __, symbol.respond_to?(:reverse)
  80   end
  81
  82   # It's important to realize that symbols are not "immutable
  83   # strings", though they are immutable. None of the
  84   # interesting string operations are available on symbols.
  85
  86   def test_symbols_cannot_be_concatenated
  87     # Exceptions will be pondered further farther down the path
  88     assert_raise(___) do
  89       :cats + :dogs
  90     end
  91   end
  92
  93   def test_symbols_can_be_dynamically_created
  94     assert_equal __, ("cats" + "dogs").to_sym
  95   end
  96
  97   # THINK ABOUT IT:
  98   #
  99   # Why is it not a good idea to dynamically create a lot of symbols?
 100 end