Lua talbe's pairs & ipairs & traverse loop, table.pack and table.unpack-白红宇

Lua 表有几种形式用得比较多,

一种是sequence, 一种是table, 还有一种是list.

1. sequence指没有气泡的一些元素. 例如{"hello", "nihao","yes"}是一个sequence, 索引为1开始的自增数字.

但是

{"hello", "nihao", nil, "yes"} 不算序列. 因为中间有个nil气泡.

> t = {"hello", "nihao", nil, "yes"}> for i,v in ipairs(t) do>> print (i,v)>> end1       hello2       nihao使用ipairs遍历t表只输出前两个值

2. table指key, value形式存储的表.

例如tbl = {a="nihao", b=nil, c="hello", d="yes"}

使用pairs可以遍历这个表, 会忽略value=nil的元素.

> tbl = {a="nihao", b=nil, c="hello", d="yes"}> for k,v in pairs(tbl) do>>  print(k,v)>> enda       nihaod       yesc       hello

其实pairs是调用了next(_s, _var)函数, 所以我们知道generic for语法的话, 可以直接使用next来写for循环.

> for k,v in next, tbl do>>   print(k,v)>> enda       nihaod       yesc       hello

直接调用next的效果

> =next(tbl,nil)a       nihao> return next(tbl,"a")d       yes> return next(tbl,"d")c       hello> return next(tbl,"c")nil

pairs原型

function pairs(t)  return next, t, nilend

3. list指链表.

> a = {"hello", next=nil}  -- 链表的头> a = {"nihao", next=a}  -- next指向头> a = {"yes", next=a}  -- next指向上层> a = {"ok", next=a}  -- next指向上层

打印链表的值.

> print(a[1])ok> print(a.next[1])yes> print(a.next.next[1])nihao> print(a.next.next.next[1])hello

生成一个链表和输出链表的值的例子

> list = nil>     for line in io.lines() do>>       list = {next=list, value=line}>>     endabcde^D>  l = list>     while l do>>       print(l.value)>>       l = l.next>>     endedcba

链表的generic for循环函数用法 .

iterator函数, 函数中不保存state值. 所以也称为stateless iterator

> function getnext(list, node)>>   if not node then>>     return list>>   else>>     return node.next>>   end>> end

factory 函数

> function traverse(list)>>   return getnext, list, nil>> end

使用io.lines生成链表

> list = nil> for line in io.lines() do>>   list = {val = line, next = list}>> endhelloyesdigoalhehe^D

使用factory函数循环

> for node in traverse(list) do >>   print (node.val)>> endhehedigoalyeshello

直接使用stateless iterator函数和state值循环

> for node in getnext,list do     print (node.val)endhehedigoalyeshello

table.pack 和table.unpack

table.pack把多个值打包成一个序列表.> a = table.pack("a","b","c","nil")> for i,v in ipairs(a) do>>   print (i,v)>> end1       a2       b3       c4       niltable.unpack把序列表解散成多值返回.> x,y,z = table.unpack(a)> print(x,y,z)a       b       c> x,y,z = table.unpack({a=1,b=2,c=3})  -- unpack不处理非序列表元素.> print(x,y,z)nil     nil     nil> x,y,z = table.unpack({a=1,b=2,c=3,"h","j","k"})  -- 只解包序列部分> print(x,y,z)h       j       k