Shulou(Shulou.com)06/03 Report--

Today, I will talk to you about which types of variables there are in Lua. Many people may not know much about it. In order to make you understand better, the editor has summarized the following for you. I hope you can get something according to this article.

Common command

View version

Lua-v

Enter interactive mode (ctrl+D exit)

Lua-I

Variable type

There are eight variable types in Lua

The type function can return the type of variable

> a=true > type (a) boolean

The tonumber function converts a string into a number

> tonumber (33.3) 33.3 > tonumber ('42') 42 > tonumber (' hello') nil

The string for Lua is immutable, and you can use double or single quotes.

> x = "hello" > yearly worlds'> print (XMague y) helloworld > print ("hello\ nworld") helloworld > x = "\ 65\ 66\ 67\ 0" > xABC

Use [[]] to represent a multiline string

> print ([[> > good > > or > > bad? >]]) goodorbad?

If you assign a variable to nil, the variable will be garbage collected. The garbage collection mechanism is automatic, usually without manual garbage collection, and there is a function of collectgarbage ().

False and nil are the only two false values of lua, which means that-1, which is false in PHP, is true in Lua.

Logical operator > a = (1 > 2) and 1 or 2-- equivalent to the ternary operator a = (1 > 2)? 1: 2 > a2 > not afalse > not not atrue multiple variables are assigned at the same time > x t.fghnil 42 43 > x t.fghnil 2-the variables that are not assigned are nil > x book z 1 2 nilTable type > t = {} > t.abc=33 > t.cde=44 > ttable: 0x7ffd93f0df30 > t.fghnil > t.abc33

Getting an undefined element returns nil, but trying to get an attribute under an undefined element throws an error

> t.fgh.xyzstdin:1: attempt to index a nil value (field 'fgh') stack traceback: stdin:1: in main chunk [C]: in? >

Elements under table can be any value or even a function, such as:

> t.fun=print > t.fun ('hello') hello

Similar to the array type of php, table can represent arrays and hash (dictionaries) in other languages

Note: the array of lua is not a special variable type, but only a form of table, and the index of the Lua array starts at 1, not 0.

> T1 = {1pr 2pm 3} > T1 [1] 1 > T2 = {a = 1, b = 2} > t2.a1

# take the length of the array, or you can take the ascending order of the string, but it doesn't seem to work for the table length of hash type. It will return 0. How to take it? (@ todo)

> = # t13

The table variable type can be any type supported by lua, or even a function, such as:

> t = {x=print} > t.x ('hello') hello

If you want to specify non-identifiers (non-marker?) As the key of Table, you need to express it with [].

> T2 = {[34] = 123, [true] = 321} > T2 [34] 123 > T2 [true] 321Lua operator

=

The result of all these operators is true or false

'=' check whether it is equal,'~ = 'check whether it is not equal. These two operators can act on any two values. If the two values to be compared are of different types, Lua thinks they are different. Otherwise, Lua compares whether they are equal according to their type. As an exception, nil is only equal to itself.

Lua compares table, userdata, and function by reference, that is, they are equal only if they are the same object. For example:

A = {}; a.x = 1; a.y = 0b = {}; b.x = 1; b.y = 0c = a

If you execute the above code, you can get, a = c, but a = b

Functions and closures

A closure is a function that refers to a variable defined outside the function, and the variable is not Gobal.

Dofile ('fn.lua')-- introduce a file

If there are not enough parameters when calling, the missing parameters will be assigned to nil

Such as:

Function fn (name1,name2,name3) print (name1,name2,name3) return 0endfn

Print a b nil

If there are more call parameters than defined parameters, the extra parameters will be discarded.

The treatment of the return value is similar:

Function fn (name1,name2,name3)-- print (name1,name2,name3) return 1, 2endx, print, z = fn ('axiomanageme') print (xmemyjinz)

Print the result

1 2 nil

Anonymous function

V = function () return 0 end

Local functions are often used when creating modules.

Local function hi (name) print ('hi'.. Name) end

Closure

Function adder (x) return function (y) return x + y endenda1 = adder (1) A100 = adder (100) print (A1 (3)) print (A100 (3))

Results:

4 103

Chunk

Every statement executed by lua, such as a file, a line of code, and a function can be understood as a chunk.

If dofile introduces a file chunk.lua, the contents are as follows

Local x = 123y=456return 789

Results:

> dofile ('chunk.lua') 789 > = y456 > = xnil

In interactive mode, each executable statement is a chunk, and the variable of one local is not visible in the next chunk, such as:

> local Xero3 > xnil-not visible

Unless you use; write in the same chunk.

> local yearly 4; print (4) 4 comments

There are two ways to annotate lua

Print ("hello comment")-- single-line comment function hello () print ("hello comment")-- [[this is a multiline comment]] end

/ / @ to-be-continue

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