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authorAdrian Bordinc <adrian.bordinc@gmail.com>2014-03-07 19:14:01 +0100
committerAdrian Bordinc <adrian.bordinc@gmail.com>2014-03-07 19:14:01 +0100
commiteb2a1422f7eba6d7ea7b9240720becd78a0ef04a (patch)
treed58493acbf3c50e5510bb6db30934cb7205ebb5b /lua.html.markdown
parent35acb53ee3b99f52d1b4f588200c724ce338be3a (diff)
parentd25212f0def8e0f85cac32b91c9a9196db038d2c (diff)
Merge remote-tracking branch 'upstream/master'
Diffstat (limited to 'lua.html.markdown')
-rw-r--r--lua.html.markdown151
1 files changed, 69 insertions, 82 deletions
diff --git a/lua.html.markdown b/lua.html.markdown
index bdd59999..be9f3141 100644
--- a/lua.html.markdown
+++ b/lua.html.markdown
@@ -12,15 +12,13 @@ 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"
@@ -60,8 +58,8 @@ 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'
karlSum = 0
@@ -81,10 +79,9 @@ repeat
num = num - 1
until num == 0
-
-----------------------------------------------------
+--------------------------------------------------------------------------------
-- 2. Functions.
-----------------------------------------------------
+--------------------------------------------------------------------------------
function fib(n)
if n < 2 then return n end
@@ -93,8 +90,8 @@ 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)
@@ -102,10 +99,9 @@ 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.
+-- 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.
@@ -118,16 +114,15 @@ 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.
+-- 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.
@@ -136,19 +131,16 @@ 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):
+-- 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:
@@ -164,14 +156,13 @@ 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
@@ -191,16 +182,15 @@ 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 behavior. Later we'll see
--- how metatables support js-prototypey behavior.
+-- 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}
@@ -221,10 +211,9 @@ 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
@@ -236,11 +225,12 @@ 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.
@@ -261,12 +251,12 @@ 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.
@@ -286,22 +276,20 @@ 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 = 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" 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.
-- 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:
@@ -315,17 +303,16 @@ 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
--- = 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 = Dog". So
+-- seymour.key will equal 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()
@@ -335,13 +322,13 @@ function LoudDog:new()
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
@@ -367,8 +354,8 @@ 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.
@@ -376,8 +363,8 @@ 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!