Eric Campbell Aug 14, 2025 1 min read Lua

Lua Tables and Metatables: The Building Blocks

Everything in Lua is built on tables. Understanding metatables unlocks operator overloading and inheritance.

Key Insights

Tables are Lua’s only data structure — they serve as arrays, dicts, objects, and modules
Metatables define behavior for operations like +, ==, and indexing
Prototype-based OOP is achieved through __index metamethod chaining

Tables as Everything

-- Array
local fruits = {"apple", "banana", "cherry"}

-- Dictionary
local config = {host = "localhost", port = 8080}

-- Mixed
local data = {1, 2, 3, name = "test", [99] = true}

Metatables for Operator Overloading

local Vector = {}
Vector.__index = Vector

function Vector.new(x, y)
    return setmetatable({x = x, y = y}, Vector)
end

function Vector.__add(a, b)
    return Vector.new(a.x + b.x, a.y + b.y)
end

local v = Vector.new(1, 2) + Vector.new(3, 4)  -- {x=4, y=6}

Inheritance via __index

local Animal = {}
Animal.__index = Animal

function Animal:speak() return "..." end

local Dog = setmetatable({}, {__index = Animal})
Dog.__index = Dog

function Dog:speak() return "Woof!" end