Lua之面向对象的实现

Lua本身是不支持面向对象的，但是可以利用table和元表、元方法进行面向对象的模拟！
以下是Cocos2d-lua中面向对象的实现！

class

function class(classname, ...)
    local cls = {__cname = classname}

    local supers = {...}
    for _, super in ipairs(supers) do
        local superType = type(super)
        -- 基类的类型只能是table或者function（若为nil，则无基类），其他类型是无效的
        assert(superType == "nil" or superType == "table" or superType == "function",
            string.format("class() - create class \"%s\" with invalid super class type \"%s\"",
                classname, superType))

        if superType == "function" then
            assert(cls.__create == nil,
                string.format("class() - create class \"%s\" with more than one creating function",
                    classname));
            -- if super is function, set it to __create
            cls.__create = super
        elseif superType == "table" then
            if super[".isclass"] then
                -- super is native class
                assert(cls.__create == nil,
                    string.format("class() - create class \"%s\" with more than one creating function or native class",
                        classname));
                cls.__create = function() return super:create() end
            else
                -- super is pure lua class
                cls.__supers = cls.__supers or {}
                cls.__supers[#cls.__supers + 1] = super
                if not cls.super then
                    -- set first super pure lua class as class.super
                    cls.super = super
                end
            end
        else
            error(string.format("class() - create class \"%s\" with invalid super type",
                        classname), 0)
        end
    end

    cls.__index = cls  -- cls作为元表的时候，索引为自身
    if not cls.__supers or #cls.__supers == 1 then -- 没有或者只有一个基类
        setmetatable(cls, {__index = cls.super})
    else  -- 有多个基类
        setmetatable(cls, {__index = function(_, key)
            local supers = cls.__supers
            for i = 1, #supers do
                local super = supers[i]
                if super[key] then return super[key] end
            end
        end})
    end

    if not cls.ctor then
        -- add default constructor
        cls.ctor = function() end
    end
    cls.new = function(...)
        local instance
        if cls.__create then
            instance = cls.__create(...)
        else
            instance = {}
        end
        setmetatableindex(instance, cls)  -- setmetatableindex见附录
        instance.class = cls
        instance:ctor(...)
        return instance
    end
    cls.create = function(_, ...)
        return cls.new(...)
    end

    return cls
end

Test Demo

基类：BaseClass.lua

local BaseClass = class("BaseClass")
 
function BaseClass:ctor()
    print("BaseClass:ctor")
end
 
function BaseClass:printFunc()
    print("this is BaseClass`s printFunc")
end

function BaseClass:testFunc()
    print("this is BaseClass`s testFunc")
end
 
return BaseClass

派生类：DerivativeClass.lua

local baseClass = require("BaseClass"):create()

local DerivativeClass = class("DerivativeClass", baseClass)
 
function DerivativeClass:ctor()
    print("DerivativeClass:ctor")
end
 
function DerivativeClass:printFunc()
    print("this is DerivativeClass`s printFunc")
end
 
return DerivativeClass

test：

local baseClass = require("BaseClass"):create()  -- 调用基类的默认构造函数ctor
baseClass:printFunc()  -- 调用基类的printFunc函数
 
local derivativeClass = require("DerivativeClass"):create()  -- 依次调用基类和派生类的默认构造函数
derivativeClass:printFunc()  -- 调用派生类的printFunc函数（重写基类的printFunc函数）
derivativeClass:testFunc()  -- 调用基类的testFunc函数

--[[
BaseClass:ctor
this is BaseClass`s printFunc
BaseClass:ctor
DerivativeClass:ctor
this is DerivativeClass`s printFunc
this is BaseClass`s testFunc
]]

附录

local setmetatableindex_
setmetatableindex_ = function(t, index)
    if type(t) == "userdata" then
        local peer = tolua.getpeer(t)
        if not peer then
            peer = {}
            tolua.setpeer(t, peer)
        end
        setmetatableindex_(peer, index)
    else
        local mt = getmetatable(t)
        if not mt then mt = {} end
        if not mt.__index then
            mt.__index = index
            setmetatable(t, mt)
        elseif mt.__index ~= index then
            setmetatableindex_(mt, index)
        end
    end
end
setmetatableindex = setmetatableindex_

Just Mark！