Mixins leves em CoffeeScript

A classe Mixin:

class Mixin
  @attachTo: (klass) ->
    klass::[k] = v for k,v of this.prototype when k isnt 'constructor'
    @included? klass

Editar : a versão original não testou a chave de propriedade, o que resultou no construtor original não sendo mais acessível.

Um mixin simples:

class Suspendable extends Mixin

  start: -> 
    # lazy context binding of handleFrameRequest
    unless @handleFrameRequest.bound
      f = @handleFrameRequest
      @handleFrameRequest = => f.apply this, argument
      @handleFrameRequest.bound = true

    # animation start
    unless @animated
      @lastTime = new Date()
      requestAnimationFrame @handleFrameRequest
      @animated = true

  stop: -> @animated = false if @animated

  handleFrameRequest: -> 
    if @animated
      currentTime = new Date()
      delta = currentTime - @lastTime
      @animate delta
      requestAnimationFrame @handleFrameRequest
      @lastTime = currentTime

  animate: -> # override to create your animations

Mixins parametrizados:

Equatable = (properties...) ->
  class extends Mixin
    equals: (o) -> o? and properties.every (p) =>
      if @[p].equals? then @[p].equals o[p] else o[p] is @[p]

Formattable = (classname, properties...) ->
  class extends Mixin
    toString: ->
      if properties.length is 0
        "[#{classname}]"
      else
        formattedProperties = ("#{p}=#{@[p]}" for p in properties)
        "[#{classname}(#{formattedProperties.join ', '})]"

    classname: -> classname

Decorar uma aula:

class Dummy
  Suspendable.attachTo Dummy
  Equatable('position', 'speed').attachTo Dummy
  Formattable('Dummy','position', 'speed').attachTo Dummy

  constructor: (@position, @speed) ->

  animate: (delta) ->
    @position = @position.add(@speed.scale(delta / 1000))
    # ...

Ótima maneira de embrulhar muitas inclusões de mixin:

class Rectangle
  PROPERTIES = ['x','y','width','height','rotation']

  [
    Equatable.apply(null, PROPERTIES)
    Formattable.apply(null, ['Rectangle'].concat PROPERTIES)
    Sourcable.apply(null, ['geomjs.Rectangle'].concat PROPERTIES)
    Parameterizable('rectangleFrom', {
      x: NaN
      y: NaN
      width: NaN
      height: NaN
      rotation: NaN
    })
    Cloneable,  Geometry,       Surface
    Path,       Triangulable,   Intersections
  ].forEach (mixin) -> mixin.attachTo Rectangle

#....

Edit : Para responder à sugestão de @sheerun , alguma outra maneira de embrulhar inclusões de mixins:

Por meio de uma classe de módulo base:

class Module 
  @include: (mixins...) ->
    if Object::toString.call(mixins[0]).indexOf('Array') >= 0
      mixins = mixins[0]

    mixins.forEach (mixin) -> mixin.attachTo this

class Dummy extends Module
  @include Suspendable, 
           Equatable('position', 'speed'),
           Formattable('Dummy','position', 'speed')

Ou se você não puder ou não quiser usar herança:

 include = (mixins...) ->
  if Object::toString.call(mixins[0]).indexOf('Array') >= 0
    mixins = mixins[0]

  in: (klass) -> mixins.forEach (mixin) -> mixin.attachTo klass

class Dummy extends Module
  include(
    Suspendable, 
    Equatable('position', 'speed'),
    Formattable('Dummy','position', 'speed')
  ).in Dummy