lua学习之table类型

发布时间：2020-12-14 22:19:24 所属栏目：大数据来源：网络整理

导读：关系表类型，这是一个很强大的类型。我们可以把这个类型看作是一个数组。只是 ? C 语言的数组，只能用正整数来作索引； ? 在 Lua 中，你可以用任意类型的值来作数组的索引，但这个值不能是 ? nil 。同样，在 C 语言中，数组的内容只允许一种类型；在 ? L

关系表类型，这是一个很强大的类型。我们可以把这个类型看作是一个数组。只是 ? C 语言的数组，只能用正整数来作索引；?在 Lua 中，你可以用任意类型的值来作数组的索引，但这个值不能是 ?nil 。同样，在 C 语言中，数组的内容只允许一种类型；在 ? Lua 中，你也可以用任意类型的值来作数组的内容， nil也可以。

基本介绍

注意三点：?
　　　　第一，所有元素之间，总是用逗号?"，"?隔开；
　　　　第二，所有索引值都需要用?"["和"]"?括起来；如果是字符串，还可以去掉引号和中括号；?即如果没有[]括起，则认为是字符串索引
　　　　第三，如果不写索引，则索引就会被认为是数字，并按顺序自动从?1往后编；

例如：

tt? =? { "hello"? , 33 }

value? =? 4

tab? =? {[ tt ]? =? "table" , key? =? value ,? [ "flag"? ]? =? nil ,? 11 }

print ( tab [ tt ])

print ( tab.key )

print ( tab [ 1? ])

以上写法都是对的。

look = {[www] = "ok"}这样是不对的，www没有赋值，所以默认为nil因此出错table index is nil

---

temp = 1

tab = {[temp] = 1,11}

print(tab[temp]) --此时的结果是11，因为11没有显式对应的key，因此从1开始，如果前面定义了，则覆盖其value

temp = 2

tab = {[temp] = 1,11}

temp = 1

print(tab[temp]) -- 结果是11，虽然定义时[temp] = 1,但是后来我们改变了temp的值，所以指向另外的key了?

以上可知：

1.对于字符串，在｛｝定义时，可以 key = value,也可以["flag"] = nil，索引都是string类型，对于非nil类型 变量（包括字符串） ，都可以[variable]=value的方式

2.使用table时，对于字符串，可以通过.的方式访问，也可以通过[]方式访问。tab[a]，tab[b]，只要a==b那么tab[a]可以访问到tab[b]的值

3.不管定义索引时用的是常量还是变量，最终table中value的索引key是常量，不会随变量的改变而变化该value的key

嵌套

tb11=?{tb12?=?{bool?=?true}}?-- simple,it's a table IN a table :)

-- Call magic!

print ( tb11.tb12.bool? )? -- works fine,since it's calling the key and value correctly.

print ( tab11 [ "tb12"? ]. bool? )? --same as line 33

print ( tab11.tb12? [ "bool" ])? --same as line 33

print ( tab11 [ "tb12"? ][ "bool" ])? --same as line 33

修改table的value

--Altering a table's content. Basically manipulating the values of the keys.

lucky =? { john = "chips"? , jane? = "lemonade" , jolene = "egg salad"? }

lucky.jolene? =? "fruit salad"? --changed the value to "fruit salad" instead of "egg salad"

lucky.jerry? =? "fagaso food"? -- adding a new key-value pair to the container lucky.

lucky.john? =? nil? -- remove john from giving anything or from being a key.

table的易变性

a?=?{};?b?=?a;

print(a?==?b)??--> true

c,d?=?{},{};

print(c?==?d)?-->false

table库函数使用

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

`1. table.sort (table [,comp])`

Sorts table elements in a given order,?in-place,from?table[1]?to?table[n],where?n?is the length of the table. If?comp?is given,then it must be a function that receives two table elements,and returns true when the first is less than the second (so that?not comp(a[i+1],a[i])?will be true after the sort). If?comp?is not given,then the standard Lua operator?<?is used instead.

The sort algorithm is not stable; that is,elements considered equal by the given order may have their relative positions changed by the sort.

name?=?{"you"?,"me",?"him","bill"?}

--table.sort - only works with arrays!

table.sort(name)

for?k,?v?in?ipairs(?name)?do

?????print(?k,v)

end

--table.sort uses callbacks. a function that is writtent to be called by a library function.

function?cmp(?a,?b)

?????if?string.sub(a,2?,2)?<?string.sub(b,2)?then

??????????return?true

?????else

??????????return?false

?????end

end

table.sort(name,?cmp)

for?k,v)

end

`2. table.insert (table,[pos,] value)`

Inserts element?value?at position?pos?in?table,shifting up other elements to open space,if necessary. The default value for?pos?is?n+1,where?n?is the length of the table so that a call?table.insert(t,x)?inserts?x?at the end of table?t.

--table.insert --an easy to copy a table to another table or adding elements to an array.!

foo? =? { "a"? , "c" ,? "d" }

bar? =? {}

function? printt (? table )

???? for? i = 1? ,# table? do

????????? print ( i , table? [ i? ])

???? end

end

print ( "before insert:"? )

printt ( foo )

table.insert ( foo , 2? , "b" )

print ( "after insert"? )

printt ( foo )

3. ?table.concat (table [,sep [,i [,j]]])

Given an array where all elements are strings or numbers,returns?table[i]..sep..table[i+1] ··· sep..table[j]. The default value for?sep?is the empty string,the default for?i?is 1,and the default for?j?is the length of the table. If?i?is greater than?j,returns the empty string.?

--table.concat does what it implies. Takes an array and concates to one string.

num? =? { 1? , 2 ,? 3 , 4 , 5? , 6 }

print ( table.concat? ( num? , "<" ))

`4. table.remove (table [,pos])`

Removes from?table?the element at position?pos,shifting down other elements to close the space,if necessary. Returns the value of the removed element. The default value for?pos?is?n,where?n?is the length of the table,so that a call?table.remove(t)?removes the last element of table?t.

abc?=?{"a"?,"b",?"c"}

print ( table.remove? ( abc? , 2 ))

print ( "abc length = "? ..? # abc )

`5. table.maxn (table)`

Returns the largest positive numerical index of the given table,or zero if the table has no positive numerical indices. (To do its job this function does a linear traversal of the whole table.)

--table.maxn

apple?=?{"a"?,"p",[?5]="e"}

print ( table.maxn? ( apple? ))? -- 5

duck? =? {[- 2? ]= 3 ,[-? 1 ]= 0 }

print ( table.maxn? ( duck? ))? -- 0

面向对象编程

--note for a object to work,it needs a closure(inner function with an upvalue(a local value from a higher scope))
--note: the more closures made,the slower the program would run.

function?mg1(?n)

???? local? function? get? ()

????????? return? n? ;

???? end

???? local? function? inc? ( m? )

????????n? =? n? + m? ;

???? end

???? return? { get? =? get ,? inc =? inc }

end

object? =? mg1 ( 50? )

print ( object.get? ())

print ( object [ "get"? ]())

object.inc ( 2? )

print ( object.get? ())

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

???? local? function? get? ( o? )

????????? return? o.one

???? end

???? local? function? inc? ( self? ,? two? )

????????self.one? =? self.one? +? two

???? end

???? function? mg3? ( one? )

????????? return? { one? =? one? ,? get? =? get? ,? inc? =? inc? }

???? end

end

a? =? mg3 ( 50? )

a : get ()

a.inc ( a , 2? )

print ( a : get ())

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

???? local? T? =? {};

???? function? T : get ()

????????? return? self.n? ;

???? end

???? function? T : inc ( m )

????????self.n? =? self.n? +? m? ;

???? end

???? function? mg4? (? n? )

????????? return? { n? =? n? ,? get? = T.get? ,? inc? = T.inc? }

???? end

end

c? =? mg4 ( 30? )

print ( c : get ())

c : inc ( 4? )

print ( c : get ())

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