Basic

_G

Description: Global variable that holds the global environment (all global functions/variables)

Example:

print(_G.tostring(true)) -- tostring is global, which makes it accessible via _G as well

setfenv

Description: sets the environment for a function to use, rather than _G.

Usage: setfenv(f)

Example:

function x()
    zzz.x = 5
    print() -- will not work here, the environment is not _G.
end

setfenv(x, {zzz = {x = 10}})

getfenv

Description: returns the environment in use by given function or stack level, default 1.

Usage: getfenv([f])

Example:

function x()
    zzz.x = 5
    print() -- will not work here, the environment is not _G.
end

setfenv(x, {zzz = {x = 10}})
print(getfenv(x)) -- environment is {zzz = {x = 10}}

setmetatable

Description: sets the metatable for given table

Usage: setmetatable(table, metatable)

Example:

local t = {}
setmetatable(t, {__call = print})

getmetatable

Description: gets the metatable of specified table, returning the __metatable metamethod’s value if applicable

Usage: getmetatable(table)

Example:

local t = {}
setmetatable(t, {__call = print})
print(getmetatable(t)) -- {__call = print}
setmetatable(t, {__metatable = {x = 5}})
print(getmetatable(t)) -- {x = 5}

rawset

Description: sets a value in the table at specified index without invoking any metamethods

Usage: rawset(table, index, value)

Example:

local t = {}
setmetatable(t, {__newindex = function(self, k, v)
    print('Value set at index '.. tostring(k) ..' to value '.. tostring(v))
end})

t.x = 5 -- Value set at index x to value 5
rawset(t, 'xx', 50) -- prints nothing, __newindex is not be invoked

rawget

Description: returns a value from a table at given index without invoking any metamethods

Usage: rawget(table, index)

Example:

local t = {}
setmetatable(t, {__index = function(self, k, v)
    print('Accessing value at index '.. tostring(k))
end})

print(t.x) -- Accessing value at index x
print(rawget(t, 'x')) -- nothing, __index is not invoked

rawequal

Description: compares two values using == without invoking any metamethod

Usage: rawequal(v1, v2)

Example:

local mt = {__eq = function(a, b)
    print('Checking equality ( '.. tostring(a) ..' vs '.. tostring(b) ..' )')
    return rawequal(a, b)
end}

local t = {}
setmetatable(t, mt)

local t2 = {}
setmetatable(t2, mt)

print(t == t2) -- Checking equality ( table: 00f28b00 vs table: 00f28a10 )
print(rawequal(t, t2)) -- nothing, __eq is not invoked

pairs

Description: iterator to traverse over a table in any order possible

Usage: pairs(t)

Example:

local t = {1, 2, 3}
for k, v in pairs(t) do
    print(k, v)
end

ipairs

Description: iterator to traverse over a table in sequence

Usage: ipairs(t)

Example:

local t = {1, 2, 3}
for k, v in ipairs(t) do
    print(k, v)
end

loadstring

Description: loads a Lua chunk

Usage: loadstring(string [, chunkName])

Example:

local f = loadstring([[return function() print(123) end]])
f() -- 123

loadfile

Description: loads a Lua chunk from specified file, or from standard input if filename is not specified

Usage: loadfile([filename])

Example:

-- x.lua
return function() print(123) end

-- other file.lua
local f = loadfile("x.lua")
f() -- 123

Description: returns the next key, value pair in table starting from specified index, otherwise index, is nil

Usage: next(table [, index])

Example:

local t = {1, 2, 3}
print(next(t, 2)) -- 3, 3
print(next(t)) -- 1, 1

pcall

Description: calls a function in a protected state, returning any errors if they happen, otherwise returns true if successful plus the returned values from f

Usage: pcall(f, …)

Example:

function x(n)
    return x + n
end

local success, ret = pcall(x, 5)
print(success, ret) -- false    C:\Users\user\lua_file.lua:2: attempt to perform arithmetic on a function value (global 'x')

xpcall

Description: calls a function in a protected state, using err as the error handler and returning true if no errors happen, otherwise returns false plus the result from err

Usage: xpcall(f, err)

Example:

function x(n)
    return x + n
end

local function x_error_handler(error)
  print(error)
  return 123
end

local success, ret = xpcall(x, x_error_handler)
print(success, ret)

Output:

C:\Users\user\lua_file.lua:2: attempt to perform arithmetic on a function value (global 'x')
false 123

unpack

Description: unpacks a table in sequence, starting from i and ending with j (1, #table respectively by default), returning all values from it

Usage: unpack(table [, i [, j]])

Example:

local t = {1, 2, 3, 4, 5}
print(unpack(t)) -- 1, 2, 3, 4, 5
print(unpack(t, 2, 4)) -- 2, 3, 4

type

Description: returns the data type of given value

Usage: type(value)

Example:

print(type(123)) -- number
print(type({})) -- table
print(type(nil)) -- nil
print(type('')) -- string
print(type(true)) -- boolean

tonumber

Description: converts value to a number if possible

Usage: tonumber(val [,base])

Example:

local x = '5'
print(tonumber(x)) -- 5
print(type(tonumber(x))) -- number
print(type(x)) -- string

tostring

Description: converts value to a string

Usage: tostring(val)

Example:

print(tostring({})) -- table: 00ee88a8
print(tostring(5)) -- 5

print('This is a boolean: '.. tostring(true)) -- This is a boolean: true