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This is <a href="."><em>Devhints.io cheatsheets</em></a> &mdash; a collection of cheatsheets I've written.
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<h1><span>Lua</span></h1>
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<h2 id="comments">Comments</h2>
<pre><code>-- comment
--[[ Multiline
comment ]]
</code></pre>
<h2 id="invoking-functions">Invoking functions</h2>
<pre><code>print()
print("Hi")
-- You can omit parentheses if the argument is one string or table literal
print "Hello World" &lt;--&gt; print("Hello World")
dofile 'a.lua' &lt;--&gt; dofile ('a.lua')
print [[a multi-line &lt;--&gt; print([[a multi-line
message]] message]])
f{x=10, y=20} &lt;--&gt; f({x=10, y=20})
type{} &lt;--&gt; type({})
</code></pre>
<h2 id="tables--arrays">Tables / arrays</h2>
<pre><code>t = {}
t = { a = 1, b = 2 }
t.a = function() ... end
t = { ["hello"] = 200 }
t.hello
-- Remember, arrays are also tables
array = { "a", "b", "c", "d" }
print(array[2]) -- "b" (one-indexed)
print(#array) -- 4 (length)
</code></pre>
<h2 id="loops">Loops</h2>
<pre><code>while condition do
end
for i = 1,5 do
end
for i = start,finish,delta do
end
for k,v in pairs(tab) do
end
repeat
until condition
-- Breaking out:
while x do
if condition then break end
end
</code></pre>
<h2 id="conditionals">Conditionals</h2>
<pre><code>if condition then
print("yes")
elseif condition then
print("maybe")
else
print("no")
end
</code></pre>
<h2 id="variables">Variables</h2>
<pre><code>local x = 2
two, four = 2, 4
</code></pre>
<h2 id="functions">Functions</h2>
<pre><code>function myFunction()
return 1
end
function myFunctionWithArgs(a, b)
-- ...
end
myFunction()
anonymousFunctions(function()
-- ...
end)
-- Not exported in the module
local function myPrivateFunction()
end
-- Splats
function doAction(action, ...)
print("Doing '"..action.."' to", ...)
--&gt; print("Doing 'write' to", "Shirley", "Abed")
end
doAction('write', "Shirley", "Abed")
</code></pre>
<h2 id="lookups">Lookups</h2>
<pre><code>mytable = { x = 2, y = function() .. end }
-- The same:
mytable.x
mytable['x']
-- Syntactic sugar, these are equivalent:
mytable.y(mytable)
mytable:y()
mytable.y(mytable, a, b)
mytable:y(a, b)
function X:y(z) .. end
function X.y(self, z) .. end
</code></pre>
<h2 id="metatables">Metatables</h2>
<pre><code>mt = {}
-- A metatable is simply a table with functions in it.
mt.__tostring = function() return "lol" end
mt.__add = function(b) ... end -- a + b
mt.__mul = function(b) ... end -- a * b
mt.__index = function(k) ... end -- Lookups (a[k] or a.k)
mt.__newindex = function(k, v) ... end -- Setters (a[k] = v)
-- Metatables allow you to override behavior of another table.
mytable = {}
setmetatable(mytable, mt)
print(myobject)
</code></pre>
<h2 id="classes">Classes</h2>
<pre><code>Account = {}
function Account:new(balance)
local t = setmetatable({}, { __index = Account })
-- Your constructor stuff
t.balance = (balance or 0)
return t
end
function Account:withdraw(amount)
print("Withdrawing "..amount.."...")
self.balance = self.balance - amount
self:report()
end
function Account:report()
print("Your current balance is: "..self.balance)
end
a = Account:new(9000)
a:withdraw(200) -- method call
</code></pre>
<h2 id="constants">Constants</h2>
<pre><code>nil
false
true
</code></pre>
<h2 id="operators-and-their-metatable-names">Operators (and their metatable names)</h2>
<pre><code>-- Relational (binary)
-- __eq __lt __gt __le __ge
== &lt; &gt; &lt;= &gt;=
~= -- Not equal, just like !=
-- Arithmetic (binary)
-- __add __sub __muv __div __mod __pow
+ - * / % ^
-- Arithmetic (unary)
-- __unm (unary minus)
-
-- Logic (and/or)
nil and false --&gt; nil
false and nil --&gt; false
0 and 20 --&gt; 20
10 and 20 --&gt; 20
-- Length
-- __len(array)
#array
-- Indexing
-- __index(table, key)
t[key]
t.key
-- __newindex(table, key, value)
t[key]=value
-- String concat
-- __concat(left, right)
"hello, "..name
-- Call
-- __call(func, ...)
</code></pre>
<h2 id="api-global-functions--ref">API: Global functions <a href="http://lua.gts-stolberg.de/en/Basis.php">(ref)</a></h2>
<pre><code>dofile("hello.lua")
loadfile("hello.lua")
assert(x) -- x or (raise an error)
assert(x, "failed")
type(var) -- "nil" | "number" | "string" | "boolean" | "table" | "function" | "thread" | "userdata"
-- Does /not/ invoke meta methods (__index and __newindex)
rawset(t, index, value) -- Like t[index] = value
rawget(t, index) -- Like t[index]
_G -- Global context
setfenv(1, {}) -- 1: current function, 2: caller, and so on -- {}: the new _G
pairs(t) -- iterable list of {key, value}
ipairs(t) -- iterable list of {index, value}
tonumber("34")
tonumber("8f", 16)
</code></pre>
<h2 id="api-strings">API: Strings</h2>
<pre><code>'string'..'concatenation'
s = "Hello"
s:upper()
s:lower()
s:len() -- Just like #s
s:find()
s:gfind()
s:match()
s:gmatch()
s:sub()
s:gsub()
s:rep()
s:char()
s:dump()
s:reverse()
s:byte()
s:format()
</code></pre>
<h2 id="api-tables">API: Tables</h2>
<pre><code>table.foreach(t, function(row) ... end)
table.setn
table.insert(t, 21) -- append (--&gt; t[#t+1] = 21)
table.insert(t, 4, 99)
table.getn
table.concat
table.sort
table.remove(t, 4)
</code></pre>
<h2 id="api-math-ref">API: Math <a href="http://lua-users.org/wiki/MathLibraryTutorial">(ref)</a></h2>
<pre><code>math.abs math.acos math.asin math.atan math.atan2
math.ceil math.cos math.cosh math.deg math.exp
math.floor math.fmod math.frexp math.ldexp math.log
math.log10 math.max math.min math.modf math.pow
math.rad math.random math.randomseed math.sin math.sinh
math.sqrt math.tan math.tanh
math.sqrt(144)
math
</code></pre>
<h2 id="api-misc">API: Misc</h2>
<pre><code>io.output(io.open("file.txt", "w"))
io.write(x)
io.close()
for line in io.lines("file.txt")
file = assert(io.open("file.txt", "r"))
file:read()
file:lines()
file:close()
</code></pre>
<h2 id="reference">Reference</h2>
<p>http://www.lua.org/pil/13.html
http://lua-users.org/wiki/ObjectOrientedProgramming</p>
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<strong><a href=".">Devhints.io cheatsheets</a></strong> is a collection of cheatsheets I've written over the years.
Suggestions and corrections? <a href='https://github.com/rstacruz/cheatsheets/issues/907'>Send them in</a>.
<i class='fleuron'></i>
I'm <a href="http://ricostacruz.com">Rico Sta. Cruz</a>.
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