lua5.1 和 5.2 关于 sequence 的定义变化，对#t

引子

环境 lua 5.2

a = {}
for i=1,2 do a[i] = i*3 end

a[4] = 11;
print(a[#a])

---print 11

-----------------------------------

a = {}
for i=1,3 do a[i] = i*3 end

a[5] = 11;
print(a[#a])

----print 9

---------------------------------

#a 第一个的值是4 第二个的值是3

依据我之前从书中看到的知识点来看的话 #a 第一个的值是2 第二个的值是3 才对啊

为啥呢

刚開始入门，源码部分就跳过吧，又没有合适的关键词搜索，仅仅能到大婶群里问了

一会儿大神来了给了个牛逼的解释

大婶：

5.1 和 5.2 关于 sequence 的定义有变化.

5.1 的
2.5.5 – The Length Operator

The length operator is denoted by the unary operator #. The length of a string is its number of bytes (that is,

the usual meaning of string length when each character is one byte).

The length of a table t is defined to be any integer index n such that t[n] is not nil and t[n+1] is nil;

moreover, if t[1] is nil, n can be zero. For a regular array, with non-nil values from 1 to a given n,

its length is exactly that n, the index of its last value. If the array has "holes" (that is, nil values between other non-nil values), then #t can be any of the indices that directly precedes a nil value (that is,

it may consider any such nil value as the end of the array).

5.2 的
3.4.6 – The Length Operator

The length operator is denoted by the unary prefix operator #. The length of a string is its number of bytes (that is,

the usual meaning of string length when each character is one byte).

A program can modify the behavior of the length operator for any value but strings through the __len metamethod

(see §2.4).

Unless a __len metamethod is given, the length of a table t is only defined if the table is a sequence, that is,

the set of its positive numeric keys is equal to {1..n} for some integer n. In that case, n is its length. Note that a table like

{10, 20, nil, 40}
is not a sequence, because it has the key 4 but does not have the key 3.

(So, there is no n such that the set {1..n} is equal to the set of positive numeric keys of that table.) Note, however, that non-numeric keys do not interfere with whether a table is a sequence.

从语言角度讲, lua 5.1 定义了 # 对数组取长度的约束. 而 lua 5.2 不严格定义了,仅仅说假设有 nil 就不确定

也就是说 lua 5.2 放宽了语言定义,同意实现更灵活

我:
非常高深啊我得慢慢啃

--[[高潮部分，直达G点]]

大婶:
没什么高深的, lua 5.2 说,你有 nil 就别指望 #table 对

dun悟了......................level +1

lua5.1 和 5.2 关于 sequence 的定义变化，对#table取值的影响

更多文章、技术交流、商务合作、联系博主

微信扫码或搜索：z360901061

微信扫一扫加我为好友

QQ号联系： 360901061

您的支持是博主写作最大的动力，如果您喜欢我的文章，感觉我的文章对您有帮助，请用微信扫描下面二维码支持博主2元、5元、10元、20元等您想捐的金额吧，狠狠点击下面给点支持吧，站长非常感激您！手机微信长按不能支付解决办法：请将微信支付二维码保存到相册，切换到微信，然后点击微信右上角扫一扫功能，选择支付二维码完成支付。

【本文对您有帮助就好】元

2元

5元

10元

20元

自定义