Classes

Classes

• Avoid the usage of class (@@) variables
  due to their “nasty” behavior in inheritance.
  [link]

  class Parent
    @@class_var = 'parent'

    def self.print_class_var
      puts @@class_var
    end
  end

  class Child < Parent
    @@class_var = 'child'
  end

  Parent.print_class_var # => will print "child"

As you can see all the classes in a class hierarchy actually share one
class variable. Class instance variables should usually be preferred
over class variables.

• Use def self.method to define singleton
  methods. This makes the methods more resistant to refactoring changes.
  [link]

  class TestClass
    # bad
    def TestClass.some_method
      ...
    end

    # good
    def self.some_other_method
      ...
    end

• Avoid class << self except when necessary,
  e.g. single accessors and aliased attributes.
  [link]

  class TestClass
    # bad
    class << self
      def first_method
        ...
      end

      def second_method_etc
        ...
      end
    end

    # good
    class << self
      attr_accessor :per_page
      alias_method :nwo, :find_by_name_with_owner
    end

    def self.first_method
      ...
    end

    def self.second_method_etc
      ...
    end
  end

• Indent the public, protected, and
  private methods as much the method definitions they apply to. Leave one
  blank line above and below them.[link]

  class SomeClass
    def public_method
      # ...
    end

    private

    def private_method
      # ...
    end
  end