mirror of
https://github.com/adambard/learnxinyminutes-docs.git
synced 2024-12-29 02:01:55 +03:00
Merge pull request #3410 from MegaBedder/patch-1
[lua/en] Update from gist/tylerneylon
This commit is contained in:
Divay Prakash
GitHub
commit
09b68aa58a
@ -12,13 +12,15 @@ filename: learnlua.lua
|
||||
Adding two ['s and ]'s makes it a
|
||||
multi-line comment.
|
||||
--]]
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
----------------------------------------------------
|
||||
-- 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.
|
||||
-- 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"
|
||||
@ -58,15 +60,10 @@ 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:
|
||||
-- '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'
|
||||
|
||||
-- BEWARE: this only acts as a ternary if the value returned when the condition
|
||||
-- evaluates to true is not `false` or Nil
|
||||
iAmNotFalse = (not aBoolValue) and false or true --> true
|
||||
iAmAlsoNotFalse = (not aBoolValue) and true or false --> true
|
||||
|
||||
karlSum = 0
|
||||
for i = 1, 100 do -- The range includes both ends.
|
||||
karlSum = karlSum + i
|
||||
@ -84,19 +81,20 @@ repeat
|
||||
num = num - 1
|
||||
until num == 0
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
----------------------------------------------------
|
||||
-- 2. Functions.
|
||||
--------------------------------------------------------------------------------
|
||||
----------------------------------------------------
|
||||
|
||||
function fib(n)
|
||||
if n < 2 then return n end
|
||||
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:
|
||||
-- The returned function is created when adder is
|
||||
-- called, and remembers the value of x:
|
||||
return function (y) return x + y end
|
||||
end
|
||||
a1 = adder(9)
|
||||
@ -104,9 +102,10 @@ 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.
|
||||
-- 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.
|
||||
@ -119,15 +118,13 @@ 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:
|
||||
-- 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 = function(x) return math.sin(x) end
|
||||
-- Equivalent to local function g(x)..., except referring to g in the function
|
||||
-- body won't work as expected.
|
||||
local g; g = function (x) return math.sin(x) end
|
||||
-- the 'local g' decl makes g-self-references ok.
|
||||
|
||||
@ -136,16 +133,15 @@ local g; g = function (x) return math.sin(x) end
|
||||
-- Calls with one string param don't need parens:
|
||||
print 'hello' -- Works fine.
|
||||
|
||||
-- Calls with one table param don't need parens either (more on tables below):
|
||||
print {} -- Works fine too.
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
----------------------------------------------------
|
||||
-- 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.
|
||||
-- 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:
|
||||
|
||||
@ -161,13 +157,14 @@ t.key2 = nil -- Removes key2 from the table.
|
||||
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.
|
||||
-- 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.
|
||||
-- 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
|
||||
@ -187,15 +184,16 @@ 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.
|
||||
-- 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
|
||||
-- behaviour. Later we'll see how metatables support js-prototype behaviour.
|
||||
-- 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}
|
||||
@ -205,7 +203,7 @@ f2 = {a = 2, b = 3}
|
||||
|
||||
metafraction = {}
|
||||
function metafraction.__add(f1, f2)
|
||||
local sum = {}
|
||||
sum = {}
|
||||
sum.b = f1.b * f2.b
|
||||
sum.a = f1.a * f2.b + f2.a * f1.b
|
||||
return sum
|
||||
@ -216,9 +214,10 @@ 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.
|
||||
-- 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
|
||||
@ -230,12 +229,11 @@ 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.
|
||||
-- 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.
|
||||
-- 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.
|
||||
@ -256,19 +254,19 @@ eatenBy = myFavs.animal -- works! thanks, metatable
|
||||
-- __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.
|
||||
-- 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.
|
||||
local newObj = {sound = 'woof'} -- 3.
|
||||
newObj = {sound = 'woof'} -- 3.
|
||||
self.__index = self -- 4.
|
||||
return setmetatable(newObj, self) -- 5.
|
||||
end
|
||||
@ -281,59 +279,62 @@ 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.
|
||||
-- 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" is 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.
|
||||
-- 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.
|
||||
-- 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()
|
||||
local s = self.sound .. ' ' -- 2.
|
||||
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 = Dog". So
|
||||
-- seymour.key will equal seymour.key, LoudDog.key, Dog.key, whichever
|
||||
-- 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)".
|
||||
-- 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()
|
||||
local newObj = {}
|
||||
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.
|
||||
--[[ I'm commenting out this section so the rest of
|
||||
-- this script remains runnable.
|
||||
```
|
||||
|
||||
```lua
|
||||
@ -359,8 +360,8 @@ local mod = require('mod') -- Run the file mod.lua.
|
||||
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.
|
||||
-- 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.
|
||||
@ -368,19 +369,19 @@ 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.
|
||||
-- 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') --> Hi!
|
||||
dofile('mod2') --> Hi! (runs again, unlike require)
|
||||
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') -- Calling f() runs mod2.lua.
|
||||
f = loadfile('mod2.lua') -- Call f() to run it.
|
||||
|
||||
-- loadstring is loadfile for strings.
|
||||
g = loadstring('print(343)') -- Returns a function.
|
||||
|
||||
Loading…
Reference in New Issue
Block a user