about_to_str.rb

require File.expand_path(File.dirname(__FILE__) + '/neo')

class AboutToStr < Neo::Koan

  class CanNotBeTreatedAsString
    def to_s
      "non-string-like"
    end
  end

  def test_to_s_returns_a_string_representation
    not_like_a_string = CanNotBeTreatedAsString.new
    assert_equal "non-string-like", not_like_a_string.to_s
  end

  def test_normally_objects_cannot_be_used_where_strings_are_expected
    assert_raise(TypeError) do
      File.exist?(CanNotBeTreatedAsString.new)
    end
  end

  # ------------------------------------------------------------------

  class CanBeTreatedAsString
    def to_s
      "string-like"
    end

    def to_str
      to_s
    end
  end

  def test_to_str_also_returns_a_string_representation
    like_a_string = CanBeTreatedAsString.new
    assert_equal "string-like", like_a_string.to_str
  end

  def test_to_str_allows_objects_to_be_treated_as_strings
    assert_equal false, File.exist?(CanBeTreatedAsString.new)
  end

  # ------------------------------------------------------------------

  def acts_like_a_string?(string)
    string = string.to_str if string.respond_to?(:to_str)
    string.is_a?(String)
  end

  def test_user_defined_code_can_check_for_to_str
    assert_equal false, acts_like_a_string?(CanNotBeTreatedAsString.new)
    assert_equal true,  acts_like_a_string?(CanBeTreatedAsString.new)
  end

  # IMPORTANT:
  # => You should not implement to_str unless your object acts like a string, rather than just having a string representation. The only core class that implements to_str is String itself.
  # REFERENCE
    # http://stackoverflow.com/questions/11182052/to-s-vs-to-str-and-to-i-to-a-vs-to-int-to-ary-in-ruby
    # http://briancarper.net/blog/98/
    # http://brettu.com/ruby-daily-ruby-tips-152-rubys-to_s-versus-to_str-methods/
end