Lua 中使用面向对象（续）

newproxy

newproxy (boolean or proxy)

Undocumented feature of Lua.

Arguments: boolean - returned proxy has metatable or userdata - different proxy created with newproxy

Creates a blank userdata with an empty metatable, or with the metatable of another proxy. Note that, in ROBLOX, creating a proxy with another proxy is disabled and will error.

local a = newproxy(true) 
local mt = getmetatable(a) 
print( mt ~= nil )
 
local b = newproxy(a) 
print( mt == getmetatable(b) )
 
local c = newproxy(false) 
print( getmetatable(c) ~= nil )
 
print( a.Name )
mt.__index = {Name="Proxy"} 
print( a.Name )
print( b.Name )

-- Output:
true
true
false
attempt to index local ‘a‘ (a userdata value)
Proxy
Proxy

-- Get current version number.
local _, _, majorv, minorv, rev = string.find(_VERSION, "(%d).(%d)[.]?([%d]?)")
local VersionNumber = tonumber(majorv) * 100 + tonumber(minorv) * 10 + (((string.len(rev) == 0) and 0) or tonumber(rev))

-- Declare current version number.
TX_VERSION = VersionNumber
TX_VERSION_510 = 510
TX_VERSION_520 = 520
TX_VERSION_530 = 530

-- The hold all class type.
local __TxClassTypeList = {}

-- The inherit class function.
local function TxClass(TypeName, SuperType)
    -- Create new class type.
    local ClassType = {}

    -- Set class type property.
    ClassType.TypeName = TypeName
    ClassType.Constructor = false
    ClassType.SuperType = SuperType

    -- The new alloc function of this class.
    ClassType.new = function (...)
        -- Create a new object first and set metatable.
        local Obj = {}

        -- Give a tostring method.
        Obj.ToString = function (self)
            local str = tostring(self)
            local _, _, addr = string.find(str, "table%s*:%s*(0?[xX]?%x+)")
            return ClassType.TypeName .. ":" .. addr
        end

        -- Do constructor recursively.
        local CreateObj = function (Class, Object, ...)
            local Create
            Create = function (c, ...)
                if c.SuperType then
                    Create(c.SuperType, ...)
                end

                if c.Constructor then
                    c.Constructor(Object, ...)
                end
            end

            Create(Class, ...)
        end

        -- Do destructor recursively.
        local ReleaseObj = function (Class, Object)
            local Release
            Release = function (c)
                if c.Destructor then
                    c.Destructor(Object)
                end

                if c.SuperType then
                    Release(c.SuperType)
                end
            end

            Release(Class)
        end

        -- Do the destructor by lua version.
        if TX_VERSION < TX_VERSION_520 then
            -- Create a empty userdata with empty metatable.
            -- And mark gc method for destructor.
            local Proxy = newproxy(true)
            getmetatable(Proxy).__gc = function (o)
                ReleaseObj(ClassType, Obj)
            end

            -- Hold the one and only reference to the proxy userdata.
            Obj.__gc = Proxy

            -- Set metatable.
            setmetatable(Obj, {__index = __TxClassTypeList[ClassType]})
        else
            -- Directly set __gc field of the metatable for destructor of this object.
            setmetatable(Obj, 
            {
                __index = __TxClassTypeList[ClassType],

                __gc = function (o)
                    ReleaseObj(ClassType, o)
                end
            })
        end

        -- Do constructor for this object.
        CreateObj(ClassType, Obj, ...)
        return Obj
    end

    -- Give a ToString method.
    ClassType.ToString = function (self)
        return self.TypeName
    end

    -- The super class type of this class.
    if SuperType then
        ClassType.super = setmetatable({}, 
        {
            __index = function (t, k)
                local Func = __TxClassTypeList[SuperType][k]
                if "function" == type(Func) then
                    t[k] = Func
                    return Func
                else
                    error("Accessing super class field are not allowed!")
                end
            end
        })
    end

    -- Virtual table
    local Vtbl = {}
    __TxClassTypeList[ClassType] = Vtbl
 
    -- Set index and new index of ClassType, and provide a default create method.
    setmetatable(ClassType,
    {
        __index = function (t, k)
            return Vtbl[k]
        end,

        __newindex = function (t, k, v)
            Vtbl[k] = v
        end,

        __call = function (self, ...)
            return ClassType.new(...)
        end
    })
 
    -- To copy super class things that this class not have.
    if SuperType then
        setmetatable(Vtbl,
        {
            __index = function (t, k)
                local Ret = __TxClassTypeList[SuperType][k]
                Vtbl[k] = Ret
                return Ret
            end
        })
    end
 
    return ClassType
end

local MyBase = TxClass("MyBase")

function MyBase:Constructor()
    print("MyBase:Constructor")
end

function MyBase:Destructor()
    print("MyBase:Destructor")
end

local MyNew = TxClass("MyNew", MyBase)

function MyNew:Constructor()
    print("MyNew:Constructor")
end

function MyNew:Destructor()
    print("MyNew:Destructor")
end

local cls = MyNew()
cls = nil
collectgarbage()

-- Output:
MyBase:Constructor
MyNew:Constructor
MyNew:Destructor
MyBase:Destructor