Current progress

koans/about_symbols.rb

@@ -0,0 +1,100 @@
+require File.expand_path(File.dirname(__FILE__) + '/neo')
+
+class AboutSymbols < Neo::Koan
+  def test_symbols_are_symbols
+    symbol = :ruby
+    assert_equal true, symbol.is_a?(Symbol)
+  end
+
+  def test_symbols_can_be_compared
+    symbol1 = :a_symbol
+    symbol2 = :a_symbol
+    symbol3 = :something_else
+
+    assert_equal true, symbol1 == symbol2
+    assert_equal false, symbol1 == symbol3
+  end
+
+  def test_identical_symbols_are_a_single_internal_object
+    symbol1 = :a_symbol
+    symbol2 = :a_symbol
+
+    assert_equal true, symbol1           == symbol2
+    assert_equal true, symbol1.object_id == symbol2.object_id
+  end
+
+  def test_method_names_become_symbols
+    symbols_as_strings = Symbol.all_symbols.map { |x| x.to_s }
+    assert_equal true, symbols_as_strings.include?("test_method_names_become_symbols")
+  end
+
+  # THINK ABOUT IT:
+  #
+  # Why do we convert the list of symbols to strings and then compare
+  # against the string value rather than against symbols?
+
+  in_ruby_version("mri") do
+    RubyConstant = "What is the sound of one hand clapping?"
+    def test_constants_become_symbols
+      all_symbols_as_strings = Symbol.all_symbols.map { |x| x.to_s }
+
+      assert_equal true, all_symbols_as_strings.include?("RubyConstant")
+    end
+  end
+
+  def test_symbols_can_be_made_from_strings
+    string = "catsAndDogs"
+    assert_equal :catsAndDogs, string.to_sym
+  end
+
+  def test_symbols_with_spaces_can_be_built
+    symbol = :"cats and dogs"
+
+    assert_equal symbol.to_sym, symbol
+  end
+
+  def test_symbols_with_interpolation_can_be_built
+    value = "and"
+    symbol = :"cats #{value} dogs"
+
+    assert_equal 'cats and dogs'.to_sym, symbol
+  end
+
+  def test_to_s_is_called_on_interpolated_symbols
+    symbol = :cats
+    string = "It is raining #{symbol} and dogs."
+
+    assert_equal 'It is raining cats and dogs.', string
+  end
+
+  def test_symbols_are_not_strings
+    symbol = :ruby
+    assert_equal false, symbol.is_a?(String)
+    assert_equal false, symbol.eql?("ruby")
+  end
+
+  def test_symbols_do_not_have_string_methods
+    symbol = :not_a_string
+    assert_equal false, symbol.respond_to?(:each_char)
+    assert_equal false, symbol.respond_to?(:reverse)
+  end
+
+  # It's important to realize that symbols are not "immutable
+  # strings", though they are immutable. None of the
+  # interesting string operations are available on symbols.
+
+  def test_symbols_cannot_be_concatenated
+    # Exceptions will be pondered further down the path
+    assert_raise(NoMethodError) do
+      :cats + :dogs
+    end
+  end
+
+  def test_symbols_can_be_dynamically_created
+    assert_equal :catsdogs, ("cats" + "dogs").to_sym
+  end
+
+  # THINK ABOUT IT:
+  #
+  # Why is it not a good idea to dynamically create a lot of symbols?
+end