Update README.md

README.md

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-# lua-cheatsheet
- a simple cheatsheet for lua
+# du-lua-cheatsheet
+ a simple cheatsheet for lua in Dual Universe
+
+## Menu
+
+* [Comments](#comments)
+* [invoking functions](#invoking-functions)
+* [Tables / arrays](#tables--arrays)
+* [Loops](#loops)
+* [Conditions](#conditions)
+* [variables](#variables)
+* [Functions](#functions)
+* [Lookups](#lookups)
+* [Metatables](#metatables)
+* [classes](#classes)
+* [constants](#constants)
+* [operators and thei metatable names](#operators-and-thei-metatable-names)
+* [API Global Functions](#api-global-functions)
+* [API Strings](#api-strings)
+* [Coroutine](#coroutine)
+
+# Lua Cheatsheet
+
+## Comments
+
+```lua
+-- comment
+
+--[[
+    multiline
+    comment
+]]
+```
+
+## invoking functions
+
+```lua
+system.print()
+system.print("Hi")
+
+-- You can omit parentheses if the argument is one string or table literal
+system.print "Hello World"     <->     system.print("Hello World")
+f{x=10, y=20}                  <->     f({x=10, y=20})
+type{}                         <->     type({})
+```
+
+## Tables / arrays
+
+```lua
+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" }
+system.print(array[2])       -- "b" (one-indexed)
+system.print(#array)         -- 4 (length)
+
+
+-- API functions
+table.foreach(t, function(row) ... end)       -- Iterates over the table
+table.setn(t, 10)                             -- Sets the length of the table
+table.insert(t, 21)                           -- append (--> t[#t+1] = 21)
+table.insert(t, 4, 99)                        -- insert (--> t[4] = 99)
+table.getn(t)                                 -- length (--> #t)
+table.concat(t, ", ")                         -- join (--> "a, b, c, d")
+table.sort(t)                                 -- sort (--> { "a", "b", "c", "d" }
+table.sort(t, function(a,b) return a > b end) -- sort (--> { "d", "c", "b", "a" }
+table.remove(t, 4)                            -- remove (--> "d")
+```
+
+## Loops
+
+```lua
+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
+```
+
+## Conditions
+
+```lua
+if condition then
+  system.print("yes")
+elseif condition then
+  system.print("maybe")
+else
+  system.print("no")
+end
+```
+
+# variables
+
+```lua
+local x = 2
+two = 2
+two, four = 2, 4
+```
+
+## Functions
+
+```lua
+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, ...)
+  system.print("Doing '"..action.."' to", ...) -- "Doing 'write' to", "Shirley", "Abed"
+end
+
+doAction('write', "Shirley", "Abed")
+```
+
+## Lookups
+
+```lua
+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
+```
+
+-- Metatables
+
+```lua
+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)
+
+system.print(myobject)
+```
+
+## classes
+
+```lua
+-- A class is simply a table with a metatable.
+-- The metatable is used to create new instances of the class.
+-- The metatable's __index is used to lookup methods on the class.
+
+-- Create a new class
+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()
+  system.print("Your current balance is: "..self.balance)
+end
+
+a = Account:new(9000)
+a:withdraw(200)    -- method call
+
+```
+
+## constants
+
+```lua
+nil
+false
+true
+```
+
+## operators and thei metatable names
+
+```lua
+-- Relational (binary)
+-- __eq  __lt  __gt  __le  __ge
+   ==    <     >     <=    >=
+~=   -- Not equal, just like !=
+
+-- Arithmetic (binary)
+-- __add  __sub  __muv  __div  __mod  __pow
+   +      -      *      /      %      ^
+
+-- Arithmetic (unary)
+-- __unm (unary minus)
+   -
+
+-- Logic (and/or)
+nil and false  --> nil
+false and nil  --> false
+0 and 20       --> 20
+10 and 20      --> 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, ...)
+```
+
+## API Global Functions
+
+```lua
+assert(x) -- Throws an error if x is false
+assert(x, "failed") -- Throws an error if x is false, with the message "failed"
+
+type(x) -- Returns the type of x ("nil" | "number" | "string" | "boolean" | "table" | "function" | "thread")
+
+-- 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") -- 34
+tonumber("8f", 16) -- 143
+```
+
+## API: Strings
+
+```lua
+'string'..'concatenation' -- "stringconcatenation"
+
+s = "Hello"
+s:upper()            -- Just like string.upper(s): "HELLO"
+s:lower()            -- Just like string.lower(s): "hello"
+s:len()              -- Just like #s or string.len(s): 5
+
+s:find("e")          -- Just like string.find(s, "e"): 2 index (in lua index start ar 1, not 0) or nil if not found
+s:gfind("l")         -- Just like string.gfind(s, "l"): iterator of all "l" in s or nil if not found
+
+s:match("e")         -- Just like string.match(s, "e"): "e" or nil if not found
+s:gmatch("l")        -- Just like string.gmatch(s, "l"): iterator of all "l" in s or nil if not found
+
+s:sub(2, 4)          -- Just like string.sub(s, 2, 4): "ell"
+s:gsub("l", "i", 10) -- Just like string.gsub(s, "l", "i", 10): "Heiio" (10 is the number of replacement)
+
+s:rep(10)            -- Just like string.rep(s, 10): "HelloHelloHelloHelloHelloHelloHelloHelloHelloHello"
+s:char(65)           -- Just like string.char(65): "A"
+s:reverse()          -- Just like string.reverse(s): "olleH"
+s:byte()             -- Just like string.byte(s): 72 (the first byte of the string)
+s:format("%s world") -- Just like string.format("%s world", s): "Hello world"
+```
+
+## Coroutine
+
+```lua
+-- A coroutine is a function that can be paused and resumed.
+-- It is useful for implementing cooperative multitasking.
+
+-- Create a new coroutine
+co = coroutine.create(function() --[[do something]] end)
+
+-- Resume a coroutine
+coroutine.resume(co) -- true | false, error
+
+-- Yield a coroutine
+coroutine.yield()
+
+-- Get the status of a coroutine
+coroutine.status(co) -- "running" | "suspended" | "dead"
+
+-- example
+co = coroutine.create(function()
+  for i = 1, 10 do
+    system.print(i) -- print 1 to 10
+    coroutine.yield() -- pause
+  end
+end)
+
+coroutine.resume(co) -- 1
+coroutine.resume(co) -- 2
+coroutine.resume(co) -- 3
+coroutine.resume(co) -- 4
+coroutine.resume(co) -- 5
+-- ...
+
+```