Editing Lua (section)

==== Inheritance ====
Lua supports using metatables to give Lua class inheritance.<ref>{{cite book|title=Programming in Lua, 4th Edition|page=165|author=Roberto Ierusalimschy}}</ref> In this example, we allow vectors to have their values multiplied by a constant in a derived class.

<syntaxhighlight lang="lua">
local Vector = {}
Vector.__index = Vector

function Vector:new(x, y, z)    -- The constructor
  -- Here, self refers to whatever class's "new"
  -- method we call.  In a derived class, self will
  -- be the derived class; in the Vector class, self
  -- will be Vector
  return setmetatable({x = x, y = y, z = z}, self)
end

function Vector:magnitude()     -- Another method
  -- Reference the implicit object using self
  return math.sqrt(self.x^2 + self.y^2 + self.z^2)
end

-- Example of class inheritance
local VectorMult = {}
VectorMult.__index = VectorMult
setmetatable(VectorMult, Vector) -- Make VectorMult a child of Vector

function VectorMult:multiply(value) 
  self.x = self.x * value
  self.y = self.y * value
  self.z = self.z * value
  return self
end

local vec = VectorMult:new(0, 1, 0) -- Create a vector
print(vec:magnitude())          -- Call a method (output: 1)
print(vec.y)                    -- Access a member variable (output: 1)
vec:multiply(2)                 -- Multiply all components of vector by 2
print(vec.y)                    -- Access member again (output: 2)
</syntaxhighlight>

Lua also supports [[multiple inheritance]]; {{code|language=lua|__index}} can either be a function or a table.<ref>{{Cite web|title=Programming in Lua : 16.3|url=https://www.lua.org/pil/16.3.html|access-date=2021-09-16|website=Lua}}</ref> [[Operator overloading]] can also be done; Lua metatables can have elements such as {{code|language=lua|__add}}, {{code|language=lua|__sub}} and so on.<ref>{{Cite web|title= Metamethods Tutorial|url=http://lua-users.org/wiki/MetamethodsTutorial|access-date=2021-09-16|website=lua-users wiki |url-status=dead |archive-url=https://web.archive.org/web/20210916182214/http://lua-users.org/wiki/MetamethodsTutorial |archive-date=September 16, 2021}}</ref>