Example for this post: http://marcoonroad.github.io/Kinds-of-Delegation

example.lua

local prototype = require 'prototype'

local point = prototype: clone { x = 0, y = 0, }

function point: move (x, y)
  self.x = self.x + x
  self.y = self.y + y
end

function point: pretty ( )
  local format = "(%d, %d)"

  return format: format (self.x, self.y)
end

local printable = { }

function printable: print ( )
  print (self: pretty ( ))
end

local instance  = point: clone { protected = false, }
local extension = instance: extend (printable)

extension: print ( )
extension: move (5, 15)
extension: print ( )