类的实现

lua中其实是没有类的，有的只是表(table)，而类之间的继承也就是将父类的表连到了一起，派生类中没有找到的属性和方法就通过元表查找父类

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

    local supers = {...}
    for _, super in ipairs(supers) do
        local superType = type(super)
        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
    if not cls.__supers or #cls.__supers == 1 then
        setmetatable(cls, {__index = cls.super})
    else
        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)
        instance.class = cls
        instance:ctor(...)
        return instance
    end
    cls.create = function(_, ...)
        return cls.new(...)
    end

    return cls
end

上面是cocos官方对class的实现
ctor是他的构造函数
可以用new或者create去实例化

类的运用

local dog = class("dog")

function dog:ctor ( ... )
    print("构造函数")
end

function dog:eat( ... )
    print("狗吃屎")
end

local dog1 = dog.new()
dog1:eat()

这里声明一个类dog，然后调用它的方法eat。

类的继承

local dog = class("dog")

function dog:ctor ( ... )
    print("父类构造函数")
end

function dog:eat( ... )
    print("狗吃屎")
end

local Huskie = class("Huskie",dog)

function Huskie:ctor( ... )
    Huskie.super.ctor(self)
    print("子类构造函数")
end

local huskie1 = Huskie.create()
huskie1:eat()

Huskie（哈士奇）继承dog，他也拥有dog的方法eat

注意继承父类的方法需要先调用super的相应的方法，第一个参数传self。

继承多个父类

--狗
local dog = class("dog")

function dog:ctor ( ... )
    print("dog构造函数")
end

function dog:eat( ... )
    print("狗吃屎")
end

--金毛
local GoldenRetriever = class("GoldenRetriever")

function GoldenRetriever:ctor( ... )
    print("GoldenRetriever构造函数")
end

function GoldenRetriever:cry( ... )
    print("金毛哭了")
end

--哈士奇
local Huskie = class("Huskie",dog,GoldenRetriever)

function Huskie:ctor( ... )
    Huskie.super.ctor(self)
    print("子类构造函数")
end

local huskie1 = Huskie.create()
huskie1:eat()
huskie1:cry()

lua中 “...” 表示全部参数