Comments

-- Single line comment 

--[[
     Multi
     line
     comments
--]]

Display info

print('Hello world!')
-- or
print'Hello world!'

Types

There are eight basic types: nil, boolean, number, string, userdata, function, thread, and table. To check type we can use type function:

print(type("Hello world"))  -- string
print(type(7))              -- number
print(type(print))          -- function
print(type(false))          -- boolean
print(type(nil))            -- nil

it returns string:

print(type(type(7)) == 'string') -- true

tostring and tonumber

local number = 10
local strNum = tostring(num);
print(type(strNum)) -- string

local stringNumber = "10"
local num = tonumber(stringNumber)
print(type(num)) -- number

Variables

Variable declaration

a = 10         -- global variable
local b = 20   -- local variable

Variable scope

if true then
  e = 40
  --  Unlike global variables, local variables have their scope
  --  limited to the block where they are declared
  local d = 30
end

print(e)  -- 40
print(d)  -- nil

String

Single-line string

local single_quote_string = 'Hello'
local double_quote_string = "World"

Multi-line string

local multi_line_string = [[
This
multi-
line
string
]]

Logical Operators

and

print(4 and 5)         --> 5
print(nil and 13)      --> nil
print(false and 13)    --> false

or

print(4 or 5)          --> 4
print(false or 5)      --> 5

not

print(not nil)      --> true
print(not false)    --> true
print(not 0)        --> false
print(not not nil)  --> false

Conditionals

if then else

local value = 20

if value == 30 then
  print("Value is 30")
elseif value == 40 then
  print("Value is 40")
else
  print("Value is not 30 or 40, but " .. value)
end

Invert value

local isLoggedIn = false
if not isLoggedIn then
  print("Please log in!")
end

Loops

for loop

for i = 1, 100 do
  print('i is: ' .. i)
end

while loop

local num = 0

while num < 50 do
  print("num is: " .. num)
  num = num + 1
end

repeat loop

local num = 10;
repeat
  print("num is: " .. num)
  num = num - 1
until num == 0

Functions

Function with return statement

local function add(a, b)
  return a + b
end

local res = add(2, 2)
print(res) -- 4

Returning multiple results

local function nums()
  return 7, 3, 1
end

local x, y, z = nums()
print(x, y, z) --- 7 3 1

Passing function to function

local fnArgs = function (fn, arg)
  fn(arg)
end

fnArgs(print, 'Hello world!')

Closures and anonymous functions

local function adder(x)
  return function (y) return x + y end
end
local res1 = adder(7)
local res2 = adder(15)
print(res1(12))  -- 19
print(res2(18))  -- 33

Vararg

local function add(...)
  local res = 0
  local vararg = {...}
  for _,v in pairs(vararg) do
    res = res + v
  end
  return res
end

print(add(1, 2, 3, 4, 5))

Tables

Define properties

local user = { first_name = 'Oleh' }              -- Option 1: set the properties
user.second_name = 'Baranovskyi'                  -- Option 2: set the properties
print(user.first_name .. ' ' .. user.second_name) -- Oleh Baranovskyi

for key, val in pairs(user) do                    -- Iterate over the keys
  print(key, val)
end

local dynamic_key = 'name'
local animal = { [dynamic_key] = 'Pluto' }        -- Dynamic key
print(animal.name)                                -- Pluto

Remove properties

user.second_name = nil
print(user.second_name)

Using table as a list

local animals = { 'dog', 'cat', 'horse', 'pig', 'frog' }
for i = 1, #animals do  -- #animals is the size of list
  print(animals[i])
end

table.insert and table.remove

local printTable = function (t)
  print('{' .. table.concat(t, ", ") .. '}')
end

local animals = { 'dog', 'cat', 'horse', 'pig', 'frog' }

table.insert(animals, 'bird')
printTable(animals)  -- {dog, cat, horse, pig, frog, bird}

table.insert(animals, 1, 'duck')
printTable(animals)  -- {duck, dog, cat, horse, pig, frog, bird}

table.remove(animals, 1)
printTable(animals) -- {dog, cat, horse, pig, frog, bird}

Print properties with penlight

local pretty = require('pl.pretty')

local t = {
  username = 'obaranvoskyi',
  name = {
    first_name = 'Oleh',
    secondname = 'Baranovskyi',
  }
}

pretty.dump(t)

output:

{
  name = {
    first_name = "Oleh",
    secondname = "Baranovskyi"
  },
  username = "obaranvoskyi"
}

penlight can be installed with LuaRocks.

Modules

Base module

hello.lua:

local M = {}

function M.hello(name)
  print('Hello, ' .. name)
end

return M

main.lua:

local m = require('hello')
m.hello('Oleh')

Classes

Define class

Person = { name = '' }

function Person:new (o, name)
  o = o or {}
  setmetatable(o, self)
  self.__index = self
  self.name = name
  return o
end

function Person:hello()
  print('[Person] Hello, my name is ' .. self.name)
end

local person = Person:new(nil, 'Oleh')
person:hello()

Inheritance

Person = { name = '' }

function Person:new (o, name)
  o = o or {}
  setmetatable(o, self)
  self.__index = self
  self.name = name
  return o
end

function Person:hello()
  print('[Person] Hello, my name is ' .. self.name)
end

local person = Person:new(nil, 'Oleh')
person:hello()


Developer = Person:new()

function Developer:new (o, name, language)
  o = o or Person:new(o, name)
  setmetatable(o, self)
  self.__index = self
  self.language = language
  return o
end

-- We override `hello` method for Developer
function Developer:hello()
  print('[Developer] Hello, my name is ' .. self.name)
  print('[Developer] I code on ' .. self.language)
end

local developer = Developer:new(nil, 'John', 'lua')
developer:hello()

LuaRocks

LuaRocks is the package manager for Lua modules.

Here is the list of supported commands:

for instance to install rock (module) with name penlight run the command:

luarocks install penlight

or to open documentation:

luarocks doc penlight

show rock info:

luarocks show penlight

show installed rocks:

lurocks list

to remove:

luarocks remove penlight

to setup project folder (including local dependency management):

luarocks init

More Resources:

• Lua Documentation
• LuaRocks
• LuaRocks Documentation
• LuaRocks Supported commands
• Lua project setup with LuaRocks