Prototype based languages

Prototype based languages are really nice when you want to share data across instances, but have the option to override that data.

For example, in Io you can write:

Button := Object clone do (
  background := Color clone set(0.5, 0.5, 0.5)
)

button := Button clone
button background = Color clone set(0.75, 0.75, 0.75)

If you don't assign button a color, it will look for it in the prototype. It's possible to do this in Ruby with 'class instance variables', but it's not as pretty :)

class View
  class << self
    attr :background, true
  end

  @background = [0.9375, 0.9375, 0.9375]

  def View.inherited( subclass )
    subclass.instance_variable_set(
     '@background', [0.9375, 0.9375, 0.9375] )
  end

  def background()
    if @background
      @background
    else
      self.class.background
    end
  end
end