Module:Middleclass

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Middleclass is an object-oriented library for Lua, written by Enrique García Cota (kikito) and maintained at GitHub.

If you are familiar with Object Orientation in other languages (C++, Java, Ruby … ) then you will probably find this library easy to use.

For a quick look at how to use the library see below. For the full documentation, see the wiki page on GitHub.

Quick Example[edit]

local class = require('Module:Middleclass').class

Person = class('Person') --this is the same as class('Person', Object) or Object:subclass('Person')

function Person:initialize(name)
	self.name = name
end

function Person:speak()
	return 'Hi, I am ' .. self.name ..'.'
end

AgedPerson = class('AgedPerson', Person) -- or Person:subclass('AgedPerson')
AgedPerson.static.ADULT_AGE = 18 --this is a class variable

function AgedPerson:initialize(name, age)
	Person.initialize(self, name) -- this calls the parent's constructor (Person.initialize) on self
	self.age = age
end

function AgedPerson:speak()
	local hi = Person.speak(self) -- "Hi, I am xx."
	if self.age < AgedPerson.ADULT_AGE then -- accessing a class variable from an instance method
		return hi .. '\nI am underaged.'
	else
		return hi .. '\nI am an adult.'
	end
end

local p1 = AgedPerson:new('Billy the Kid', 13) -- this is equivalent to AgedPerson('Billy the Kid', 13) - the :new part is implicit
local p2 = AgedPerson:new('Luke Skywalker', 21)
mw.log(p1:speak())
mw.log(p2:speak())

Output:

Hi, I'm Billy the Kid.
I am underaged.
Hi, I'm Luke Skywalker.
I am an adult.

Notes:[edit]

The standard way to do inheritance is class(‘A’, B). In addition to that, you can also do B:subclass(‘A’). Both expressions will return A (a subclass of B). A.super will return B.

When you call A:new(), only A:initialize() gets called – the constructor of B is not called by default. There is no super, instead you have to use an explicit self:

function A:initialize()
  ...
  B.initialize(self, ...)
  ...
end

The same applies for non-constructor methods – there is no super keyword-like construction, so you must use explicit self calls.

local middleclass = {
  _VERSION     = 'middleclass v4.0.0',
  _DESCRIPTION = 'Object Orientation for Lua',
  _URL         = 'https://github.com/kikito/middleclass',
  _LICENSE     = [[
    MIT LICENSE

    Copyright (c) 2011 Enrique García Cota

    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject to
    the following conditions:

    The above copyright notice and this permission notice shall be included
    in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
    OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
    IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
    CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
    TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
    SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  ]]
}

local function _createIndexWrapper(aClass, f)
  if f == nil then
    return aClass.__instanceDict
  else
    return function(self, name)
      local value = aClass.__instanceDict[name]

      if value ~= nil then
        return value
      elseif type(f) == "function" then
        return (f(self, name))
      else
        return f[name]
      end
    end
  end
end

local function _propagateInstanceMethod(aClass, name, f)
  f = name == "__index" and _createIndexWrapper(aClass, f) or f
  aClass.__instanceDict[name] = f

  for subclass in pairs(aClass.subclasses) do
    if rawget(subclass.__declaredMethods, name) == nil then
      _propagateInstanceMethod(subclass, name, f)
    end
  end
end

local function _declareInstanceMethod(aClass, name, f)
  aClass.__declaredMethods[name] = f

  if f == nil and aClass.super then
    f = aClass.super.__instanceDict[name]
  end

  _propagateInstanceMethod(aClass, name, f)
end

local function _tostring(self) return "class " .. self.name end
local function _call(self, ...) return self:new(...) end

local function _createClass(name, super)
  local dict = {}
  dict.__index = dict

  local aClass = { name = name, super = super, static = {},
                   __instanceDict = dict, __declaredMethods = {},
                   subclasses = setmetatable({}, {__mode='k'})  }

  if super then
    setmetatable(aClass.static, { __index = function(_,k) return rawget(dict,k) or super.static[k] end })
  else
    setmetatable(aClass.static, { __index = function(_,k) return rawget(dict,k) end })
  end

  setmetatable(aClass, { __index = aClass.static, __tostring = _tostring,
                         __call = _call, __newindex = _declareInstanceMethod })

  return aClass
end

local function _includeMixin(aClass, mixin)
  assert(type(mixin) == 'table', "mixin must be a table")

  for name,method in pairs(mixin) do
    if name ~= "included" and name ~= "static" then aClass[name] = method end
  end

  for name,method in pairs(mixin.static or {}) do
    aClass.static[name] = method
  end

  if type(mixin.included)=="function" then mixin:included(aClass) end
  return aClass
end

local DefaultMixin = {
  __tostring   = function(self) return "instance of " .. tostring(self.class) end,

  initialize   = function(self, ...) end,

  isInstanceOf = function(self, aClass)
    return type(self)       == 'table' and
           type(self.class) == 'table' and
           type(aClass)     == 'table' and
           ( aClass == self.class or
             type(aClass.isSubclassOf) == 'function' and
             self.class:isSubclassOf(aClass) )
  end,

  static = {
    allocate = function(self)
      assert(type(self) == 'table', "Make sure that you are using 'Class:allocate' instead of 'Class.allocate'")
      return setmetatable({ class = self }, self.__instanceDict)
    end,

    new = function(self, ...)
      assert(type(self) == 'table', "Make sure that you are using 'Class:new' instead of 'Class.new'")
      local instance = self:allocate()
      instance:initialize(...)
      return instance
    end,

    subclass = function(self, name)
      assert(type(self) == 'table', "Make sure that you are using 'Class:subclass' instead of 'Class.subclass'")
      assert(type(name) == "string", "You must provide a name(string) for your class")

      local subclass = _createClass(name, self)

      for methodName, f in pairs(self.__instanceDict) do
        _propagateInstanceMethod(subclass, methodName, f)
      end
      subclass.initialize = function(instance, ...) return self.initialize(instance, ...) end

      self.subclasses[subclass] = true
      self:subclassed(subclass)

      return subclass
    end,

    subclassed = function(self, other) end,

    isSubclassOf = function(self, other)
      return type(other)      == 'table' and
             type(self)       == 'table' and
             type(self.super) == 'table' and
             ( self.super == other or
               type(self.super.isSubclassOf) == 'function' and
               self.super:isSubclassOf(other) )
    end,

    include = function(self, ...)
      assert(type(self) == 'table', "Make sure you that you are using 'Class:include' instead of 'Class.include'")
      for _,mixin in ipairs({...}) do _includeMixin(self, mixin) end
      return self
    end
  }
}

function middleclass.class(name, super)
  assert(type(name) == 'string', "A name (string) is needed for the new class")
  return super and super:subclass(name) or _includeMixin(_createClass(name), DefaultMixin)
end

setmetatable(middleclass, { __call = function(_, ...) return middleclass.class(...) end })

return middleclass