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