这是否是lua变量作用域问题（以及如何解决）？

非常奇怪的错误，显示一个对象是空的。

一个人会认为，如果 pbs:HasNext() 是 true，意味着 pbs 一定不是 nil。

然而，HTMLEntityCodec:DecodeCharacter 的第一行打印了 nil：

function HTMLEntityCodec:DecodeCharacter(pbs)
    print(pbs)
    ...

完整文件如下，从 1800 多行被削减到 110 行，以便于 SO 用户可以更清晰地获取上下文。但是这种削减会将代码中的所有逻辑削减掉，所以不要被搞混了。

#!/usr/bin/env lua

function Inherits( baseClass )
    local new_class = {}
    local class_mt = { __index = new_class }

    function new_class:create()
        local newinst = {}
        setmetatable( newinst, class_mt )
        return newinst
    end

    if baseClass then
        setmetatable( new_class, { __index = baseClass } )
    end

    return new_class
end

-------------------------------------------
-- PushbackString
-------------------------------------------
PushbackString = Inherits({})

function PushbackString:Init(input)
    self.input = input
    self.pushback = nil
    self.temp = nil
    self.index = 0
    self.mark = 0
end

-- 标记当前索引，这样客户端可以在需要时重置到它。
function PushbackString:HasNext()
    return true
end

function PushbackString:Mark ()
    self.temp = self.pushback
    self.mark = self.index
end

BaseCodec = Inherits({})

function BaseCodec:Decode(input)
    local buff = ''
    local pbs = PushbackString:create()

    pbs:Init(input)

    while pbs:HasNext() do
        local char = self.DecodeCharacter(pbs)
        if char ~= nil then
            buff = buff .. char
        else
            buff = buff .. pbs:Next()
        end
    end
    return buff
end

HTMLEntityCodec = Inherits(BaseCodec)
-- HTMLEntityCodec.classname = ('HTMLEntityCodec')

function HTMLEntityCodec:DecodeCharacter(pbs)
    print(pbs)
    pbs:Mark()
end

DefaultEncoder = Inherits({})

function DefaultEncoder:Init(codecs)
    self.html_codec = HTMLEntityCodec:create()
end

function DefaultEncoder:TestInput(input , strict)
    print ("\n----------------8<----------------8<----------------\n")
    print ("Input:\t" .. input)
    -- 默认值
    if strict == nil then strict = true end

    -- 无事可做
    if input == nil then return nil end

    local working = input
    local codecs_found = {}
    local found_count = 0
    local clean = false

    while not clean do
        clean = true
        old = working
        working = self.html_codec:Decode( working )
        if old ~= working then
            print ("Warning:\tINTRUSION DETECTED")
        end
    end

    print ("Output:\t".. working)
    return working
end

local default_encoder = DefaultEncoder:create()
default_encoder:Init()
default_encoder:TestInput("%25", true)

----------8<-----------8<--------------8<----------------

文件结束。

控制台输出：

tzury@1005:~/devel/lua$ lua problem.lua

----------------8<----------------8<----------------

Input:  %25
nil
lua: problem.lua:70: attempt to index local 'pbs' (a nil value)
stack traceback:
        problem.lua:70: in function 'DecodeCharacter'
        problem.lua:54: in function 'Decode'
        problem.lua:96: in function 'TestInput'
        problem.lua:109: in main chunk
        [C]: ?