Lua: Tables — The Only Data Structure

What you will learn

Tables are Lua's single and universal data structure — they serve as arrays, dictionaries, objects, and more.

Tables as arrays (1-indexed!)

local fruits = {"apple", "banana", "cherry"}
print(fruits[1])  -- apple (1-based indexing!)
print(#fruits)     -- 3 (length operator)
table.insert(fruits, "date")    -- append
table.remove(fruits, 1)          -- remove first element

Important: Lua arrays are 1-indexed, not 0-indexed. fruits[0] returns nil.

Tables as dictionaries

local user = {
    name = "Alice",
    age = 25,
    ["email"] = "[email protected]"  -- bracket syntax also works
}
print(user.name)       -- Alice (dot notation)
print(user["name"])   -- Alice (bracket notation)
user.active = true     -- add new field
user.age = nil         -- remove a field (set to nil)

Both .name and ["name"] access fields. Use brackets when the key is stored in a variable or contains spaces.

Tables as objects (with metatables)

local person = { name = "Alice" }

function person:greet()
    print("Hi, I'm " .. self.name)
end

person:greet()  -- Hi, I'm Alice

The : syntax automatically passes self as the first argument.

Common mistakes

• Using 0-based indexing — Lua starts at 1.
• Setting a table field to nil to remove it — this is correct, but note that nil also marks the end of array sequences for #.
• Using # on a table with gaps (nil values in the array) — # is unreliable for tables with holes.
• Forgetting that tables are reference types: assignment t2 = t1 copies the reference, not the data.

Quick check below!