|
|
第1行: |
第1行: |
| -- Two dashes start a one-line comment. | | -- 定义一个模块表 |
| | local p = {} |
|
| |
|
| --[[ | | -- 添加一个简单的函数 |
| Adding two ['s and ]'s makes it a
| | function p.hello() |
| multi-line comment.
| | return "Hello, World! 这是一个简单的MediaWiki模块示例。" |
| --]]
| |
| | |
| ----------------------------------------------------
| |
| -- 1. Variables and flow control.
| |
| ----------------------------------------------------
| |
| | |
| num = 42 -- All numbers are doubles.
| |
| -- Don't freak out, 64-bit doubles have 52 bits for
| |
| -- storing exact int values; machine precision is
| |
| -- not a problem for ints that need < 52 bits.
| |
| | |
| s = 'walternate' -- Immutable strings like Python.
| |
| t = "double-quotes are also fine"
| |
| u = [[ Double brackets
| |
| start and end
| |
| multi-line strings.]]
| |
| t = nil -- Undefines t; Lua has garbage collection.
| |
| | |
| -- Blocks are denoted with keywords like do/end:
| |
| while num < 50 do
| |
| num = num + 1 -- No ++ or += type operators.
| |
| end
| |
| | |
| -- If clauses:
| |
| if num > 40 then
| |
| print('over 40')
| |
| elseif s ~= 'walternate' then -- ~= is not equals.
| |
| -- Equality check is == like Python; ok for strs.
| |
| io.write('not over 40\n') -- Defaults to stdout.
| |
| else
| |
| -- Variables are global by default.
| |
| thisIsGlobal = 5 -- Camel case is common.
| |
| | |
| -- How to make a variable local:
| |
| local line = io.read() -- Reads next stdin line.
| |
| | |
| -- String concatenation uses the .. operator:
| |
| print('Winter is coming, ' .. line)
| |
| end
| |
| | |
| -- Undefined variables return nil.
| |
| -- This is not an error:
| |
| foo = anUnknownVariable -- Now foo = nil.
| |
| | |
| aBoolValue = false
| |
| | |
| -- Only nil and false are falsy; 0 and '' are true!
| |
| if not aBoolValue then print('twas false') end
| |
| | |
| -- 'or' and 'and' are short-circuited.
| |
| -- This is similar to the a?b:c operator in C/js:
| |
| ans = aBoolValue and 'yes' or 'no' --> 'no'
| |
| | |
| karlSum = 0
| |
| for i = 1, 100 do -- The range includes both ends.
| |
| karlSum = karlSum + i
| |
| end
| |
| | |
| -- Use "100, 1, -1" as the range to count down:
| |
| fredSum = 0
| |
| for j = 100, 1, -1 do fredSum = fredSum + j end
| |
| | |
| -- In general, the range is begin, end[, step].
| |
| | |
| -- Another loop construct:
| |
| repeat
| |
| print('the way of the future')
| |
| num = num - 1
| |
| until num == 0
| |
| | |
| | |
| ----------------------------------------------------
| |
| -- 2. Functions.
| |
| ----------------------------------------------------
| |
| | |
| function fib(n)
| |
| if n < 2 then return 1 end
| |
| return fib(n - 2) + fib(n - 1)
| |
| end
| |
| | |
| -- Closures and anonymous functions are ok:
| |
| function adder(x)
| |
| -- The returned function is created when adder is
| |
| -- called, and remembers the value of x:
| |
| return function (y) return x + y end
| |
| end | | end |
| a1 = adder(9)
| |
| a2 = adder(36)
| |
| print(a1(16)) --> 25
| |
| print(a2(64)) --> 100
| |
|
| |
| -- Returns, func calls, and assignments all work
| |
| -- with lists that may be mismatched in length.
| |
| -- Unmatched receivers are nil;
| |
| -- unmatched senders are discarded.
| |
|
| |
| x, y, z = 1, 2, 3, 4
| |
| -- Now x = 1, y = 2, z = 3, and 4 is thrown away.
| |
|
| |
| function bar(a, b, c)
| |
| print(a, b, c)
| |
| return 4, 8, 15, 16, 23, 42
| |
| end
| |
|
| |
| x, y = bar('zaphod') --> prints "zaphod nil nil"
| |
| -- Now x = 4, y = 8, values 15..42 are discarded.
| |
|
| |
| -- Functions are first-class, may be local/global.
| |
| -- These are the same:
| |
| function f(x) return x * x end
| |
| f = function (x) return x * x end
| |
|
| |
| -- And so are these:
| |
| local function g(x) return math.sin(x) end
| |
| local g; g = function (x) return math.sin(x) end
| |
| -- the 'local g' decl makes g-self-references ok.
| |
|
| |
| -- Trig funcs work in radians, by the way.
| |
|
| |
| -- Calls with one string param don't need parens:
| |
| print 'hello' -- Works fine.
| |
|
| |
|
| |
| ----------------------------------------------------
| |
| -- 3. Tables.
| |
| ----------------------------------------------------
| |
|
| |
| -- Tables = Lua's only compound data structure;
| |
| -- they are associative arrays.
| |
| -- Similar to php arrays or js objects, they are
| |
| -- hash-lookup dicts that can also be used as lists.
| |
|
| |
| -- Using tables as dictionaries / maps:
| |
|
| |
| -- Dict literals have string keys by default:
| |
| t = {key1 = 'value1', key2 = false}
| |
|
| |
| -- String keys can use js-like dot notation:
| |
| print(t.key1) -- Prints 'value1'.
| |
| t.newKey = {} -- Adds a new key/value pair.
| |
| t.key2 = nil -- Removes key2 from the table.
| |
|
| |
| -- Literal notation for any (non-nil) value as key:
| |
| u = {['@!#'] = 'qbert', [{}] = 1729, [6.28] = 'tau'}
| |
| print(u[6.28]) -- prints "tau"
| |
|
| |
| -- Key matching is basically by value for numbers
| |
| -- and strings, but by identity for tables.
| |
| a = u['@!#'] -- Now a = 'qbert'.
| |
| b = u[{}] -- We might expect 1729, but it's nil:
| |
| -- b = nil since the lookup fails. It fails
| |
| -- because the key we used is not the same object
| |
| -- as the one used to store the original value. So
| |
| -- strings & numbers are more portable keys.
| |
|
| |
| -- A one-table-param function call needs no parens:
| |
| function h(x) print(x.key1) end
| |
| h{key1 = 'Sonmi~451'} -- Prints 'Sonmi~451'.
| |
|
| |
| for key, val in pairs(u) do -- Table iteration.
| |
| print(key, val)
| |
| end
| |
|
| |
| -- _G is a special table of all globals.
| |
| print(_G['_G'] == _G) -- Prints 'true'.
| |
|
| |
| -- Using tables as lists / arrays:
| |
|
| |
| -- List literals implicitly set up int keys:
| |
| v = {'value1', 'value2', 1.21, 'gigawatts'}
| |
| for i = 1, #v do -- #v is the size of v for lists.
| |
| print(v[i]) -- Indices start at 1 !! SO CRAZY!
| |
| end
| |
| -- A 'list' is not a real type. v is just a table
| |
| -- with consecutive integer keys, treated as a list.
| |
|
| |
| ----------------------------------------------------
| |
| -- 3.1 Metatables and metamethods.
| |
| ----------------------------------------------------
| |
|
| |
| -- A table can have a metatable that gives the table
| |
| -- operator-overloadish behavior. Later we'll see
| |
| -- how metatables support js-prototypey behavior.
| |
|
| |
| f1 = {a = 1, b = 2} -- Represents the fraction a/b.
| |
| f2 = {a = 2, b = 3}
| |
|
| |
| -- This would fail:
| |
| -- s = f1 + f2
| |
|
| |
| metafraction = {}
| |
| function metafraction.__add(f1, f2)
| |
| sum = {}
| |
| sum.b = f1.b * f2.b
| |
| sum.a = f1.a * f2.b + f2.a * f1.b
| |
| return sum
| |
| end
| |
|
| |
| setmetatable(f1, metafraction)
| |
| setmetatable(f2, metafraction)
| |
|
| |
| s = f1 + f2 -- call __add(f1, f2) on f1's metatable
| |
|
| |
| -- f1, f2 have no key for their metatable, unlike
| |
| -- prototypes in js, so you must retrieve it as in
| |
| -- getmetatable(f1). The metatable is a normal table
| |
| -- with keys that Lua knows about, like __add.
| |
|
| |
| -- But the next line fails since s has no metatable:
| |
| -- t = s + s
| |
| -- Class-like patterns given below would fix this.
| |
|
| |
| -- An __index on a metatable overloads dot lookups:
| |
| defaultFavs = {animal = 'gru', food = 'donuts'}
| |
| myFavs = {food = 'pizza'}
| |
| setmetatable(myFavs, {__index = defaultFavs})
| |
| eatenBy = myFavs.animal -- works! thanks, metatable
| |
|
| |
| -- Direct table lookups that fail will retry using
| |
| -- the metatable's __index value, and this recurses.
| |
|
| |
| -- An __index value can also be a function(tbl, key)
| |
| -- for more customized lookups.
| |
|
| |
| -- Values of __index,add, .. are called metamethods.
| |
| -- Full list. Here a is a table with the metamethod.
| |
|
| |
| -- __add(a, b) for a + b
| |
| -- __sub(a, b) for a - b
| |
| -- __mul(a, b) for a * b
| |
| -- __div(a, b) for a / b
| |
| -- __mod(a, b) for a % b
| |
| -- __pow(a, b) for a ^ b
| |
| -- __unm(a) for -a
| |
| -- __concat(a, b) for a .. b
| |
| -- __len(a) for #a
| |
| -- __eq(a, b) for a == b
| |
| -- __lt(a, b) for a < b
| |
| -- __le(a, b) for a <= b
| |
| -- __index(a, b) <fn or a table> for a.b
| |
| -- __newindex(a, b, c) for a.b = c
| |
| -- __call(a, ...) for a(...)
| |
|
| |
| ----------------------------------------------------
| |
| -- 3.2 Class-like tables and inheritance.
| |
| ----------------------------------------------------
| |
|
| |
| -- Classes aren't built in; there are different ways
| |
| -- to make them using tables and metatables.
| |
|
| |
| -- Explanation for this example is below it.
| |
|
| |
| Dog = {} -- 1.
| |
|
| |
| function Dog:new() -- 2.
| |
| newObj = {sound = 'woof'} -- 3.
| |
| self.__index = self -- 4.
| |
| return setmetatable(newObj, self) -- 5.
| |
| end
| |
|
| |
| function Dog:makeSound() -- 6.
| |
| print('I say ' .. self.sound)
| |
| end
| |
|
| |
| mrDog = Dog:new() -- 7.
| |
| mrDog:makeSound() -- 'I say woof' -- 8.
| |
|
| |
| -- 1. Dog acts like a class; it's really a table.
| |
| -- 2. function tablename:fn(...) is the same as
| |
| -- function tablename.fn(self, ...)
| |
| -- The : just adds a first arg called self.
| |
| -- Read 7 & 8 below for how self gets its value.
| |
| -- 3. newObj will be an instance of class Dog.
| |
| -- 4. self = the class being instantiated. Often
| |
| -- self = Dog, but inheritance can change it.
| |
| -- newObj gets self's functions when we set both
| |
| -- newObj's metatable and self's __index to self.
| |
| -- 5. Reminder: setmetatable returns its first arg.
| |
| -- 6. The : works as in 2, but this time we expect
| |
| -- self to be an instance instead of a class.
| |
| -- 7. Same as Dog.new(Dog), so self = Dog in new().
| |
| -- 8. Same as mrDog.makeSound(mrDog); self = mrDog.
| |
|
| |
| ----------------------------------------------------
| |
|
| |
| -- Inheritance example:
| |
|
| |
| LoudDog = Dog:new() -- 1.
| |
|
| |
| function LoudDog:makeSound()
| |
| s = self.sound .. ' ' -- 2.
| |
| print(s .. s .. s)
| |
| end
| |
|
| |
| seymour = LoudDog:new() -- 3.
| |
| seymour:makeSound() -- 'woof woof woof' -- 4.
| |
|
| |
| -- 1. LoudDog gets Dog's methods and variables.
| |
| -- 2. self has a 'sound' key from new(), see 3.
| |
| -- 3. Same as LoudDog.new(LoudDog), and converted to
| |
| -- Dog.new(LoudDog) as LoudDog has no 'new' key,
| |
| -- but does have __index = Dog on its metatable.
| |
| -- Result: seymour's metatable is LoudDog, and
| |
| -- LoudDog.__index = LoudDog. So seymour.key will
| |
| -- = seymour.key, LoudDog.key, Dog.key, whichever
| |
| -- table is the first with the given key.
| |
| -- 4. The 'makeSound' key is found in LoudDog; this
| |
| -- is the same as LoudDog.makeSound(seymour).
| |
|
| |
| -- If needed, a subclass's new() is like the base's:
| |
| function LoudDog:new()
| |
| newObj = {}
| |
| -- set up newObj
| |
| self.__index = self
| |
| return setmetatable(newObj, self)
| |
| end
| |
|
| |
| ----------------------------------------------------
| |
| -- 4. Modules.
| |
| ----------------------------------------------------
| |
|
| |
|
| |
| --[[ I'm commenting out this section so the rest of
| |
| -- this script remains runnable.
| |
| -- Suppose the file mod.lua looks like this:
| |
| local M = {}
| |
|
| |
| local function sayMyName()
| |
| print('Hrunkner')
| |
| end
| |
|
| |
| function M.sayHello()
| |
| print('Why hello there')
| |
| sayMyName()
| |
| end
| |
|
| |
| return M
| |
|
| |
| -- Another file can use mod.lua's functionality:
| |
| local mod = require('mod') -- Run the file mod.lua.
| |
|
| |
| -- require is the standard way to include modules.
| |
| -- require acts like: (if not cached; see below)
| |
| local mod = (function ()
| |
| <contents of mod.lua>
| |
| end)()
| |
| -- It's like mod.lua is a function body, so that
| |
| -- locals inside mod.lua are invisible outside it.
| |
|
| |
| -- This works because mod here = M in mod.lua:
| |
| mod.sayHello() -- Says hello to Hrunkner.
| |
|
| |
| -- This is wrong; sayMyName only exists in mod.lua:
| |
| mod.sayMyName() -- error
| |
|
| |
| -- require's return values are cached so a file is
| |
| -- run at most once, even when require'd many times.
| |
|
| |
| -- Suppose mod2.lua contains "print('Hi!')".
| |
| local a = require('mod2') -- Prints Hi!
| |
| local b = require('mod2') -- Doesn't print; a=b.
| |
|
| |
| -- dofile is like require without caching:
| |
| dofile('mod2.lua') --> Hi!
| |
| dofile('mod2.lua') --> Hi! (runs it again)
| |
|
| |
| -- loadfile loads a lua file but doesn't run it yet.
| |
| f = loadfile('mod2.lua') -- Call f() to run it.
| |
|
| |
| -- loadstring is loadfile for strings.
| |
| g = loadstring('print(343)') -- Returns a function.
| |
| g() -- Prints out 343; nothing printed before now.
| |
|
| |
| --]]
| |
|
| |
| ----------------------------------------------------
| |
| -- 5. References.
| |
| ----------------------------------------------------
| |
|
| |
| --[[
| |
|
| |
| I was excited to learn Lua so I could make games
| |
| with the Löve 2D game engine. That's the why.
| |
|
| |
| I started with BlackBulletIV's Lua for programmers.
| |
| Next I read the official Programming in Lua book.
| |
| That's the how.
| |
|
| |
| It might be helpful to check out the Lua short
| |
| reference on lua-users.org.
| |
|
| |
| The main topics not covered are standard libraries:
| |
| * string library
| |
| * table library
| |
| * math library
| |
| * io library
| |
| * os library
| |
|
| |
| By the way, this entire file is valid Lua; save it
| |
| as learn.lua and run it with "lua learn.lua" !
| |
|
| |
| This was first written for tylerneylon.com. It's
| |
| also available as a github gist. Tutorials for other
| |
| languages, in the same style as this one, are here:
| |
|
| |
| https://learnxinyminutes.com/
| |
|
| |
| Have fun with Lua!
| |
|
| |
|
| --]] | | -- 返回模块表 |
| | return p |