Creates a class-variable attribute that can be accessed both on an instance and class level.

NOTE This used to be a Module method. But turns out it does not work as expected when included. The class-level method is not carried along. So it is now just a Class method. Accordingly, mattr has been deprecated.

CREDIT: David Heinemeier Hansson

Creates a class-variable attr_accessor that can be accessed both on an instance and class level.

  class MyClass
    cattr_accessor :a
  end

  MyClass.a = 10
  MyClass.a           #=> 10
  mc = MyClass.new
  mc.a                #=> 10

CREDIT: David Heinemeier Hansson

Creates a class-variable attr_reader that can be accessed both on an instance and class level.

  class MyClass
    @@a = 10
    cattr_reader :a
  end

  MyClass.a           #=> 10
  MyClass.new.a       #=> 10

CREDIT: David Heinemeier Hansson

Creates a class-variable attr_writer that can be accessed both on an instance and class level.

  class MyClass
    cattr_writer :a
    def a
      @@a
    end
  end

  MyClass.a = 10
  MyClass.a            #=> 10
  MyClass.new.a = 29
  MyClass.a            #=> 29

CREDIT: David Heinemeier Hansson

For Class, class_extend is the same as class_eval. The alternative is to "undef_method :class_extend", but this seems uneccessarily limited.

List all descedents of this class.

  class X ; end
  class A < X; end
  class B < X; end
  X.descendents  #=> [A,B]

NOTE: This is a intesive operation. Do not expect it to be super fast.

Translate a class name to a suitable method name.

  My::CoolClass.methodize => "my__cool_class"

Converts a class name to a unix path.

  My::CoolClass.pathize  #=> "my/cool_class"

Prepend an "aspect module" to a class.

  class Firetruck
    def put_out_fire(option)
      "Put out #{option}"
    end
  end

  module FastFiretruck
    def put_out_fire(option)
      super("very #{option}!")
    end
  end

  Firetruck.prepend(FastFiretruck)

  ft = Firetruck.new
  ft.put_out_fire('fast') #=> "Put out very fast!"

Implementation of this method has some limitations, in that it works by overriding new and allocate.

CREDIT: Trans

TODO: Perhaps rename this to preallocate, b/c of the way it works. It is not really a clean prepend, like that of Module#prepend.

Convert instatiation of a class into a Proc.

  class Person
    def initialize(name)
      @name = name
    end

    def inspect
      @name.to_str
    end
  end

  %w(john bob jane hans).map(&Person) => [john, bob, jane, hans]

CREDIT: Daniel Schierbeck