Lua 5 5 0

Lua 5.5.0

Overview

Lua is a powerful, efficient, lightweight, embeddable scripting language developed by PUC-Rio. It uses garbage-collected dynamic typing, first-class functions with lexical scoping and closures, and provides coroutines for cooperative multitasking. Lua is implemented in clean ISO C and compiles unmodified on all platforms with an ISO C compiler (also as C++).

The single core data structure is the table — an associative array supporting both array-like (integer keys) and map-like (arbitrary keys) access, with metatables for operator overloading and behavior customization.

When to Use

• Writing Lua scripts or modules for existing Lua-based systems
• Embedding Lua as a scripting engine in C/C++ applications
• Creating domain-specific languages or configuration formats
• Building game scripting, plugin systems, or runtime extensibility
• Working with Neovim plugins, OpenResty/Nginx scripting, or LÖVE2D games
• Understanding Lua 5.5 incompatibilities when migrating from 5.4

Core Concepts

Types: nil, boolean, number (doubles by default), integer (64-bit by default), string (immutable, multi-byte), table, function (first-class closures), thread (coroutines), userdata (full and light).

Tables as the sole data structure: Arrays (t[1]), maps (t["key"]), objects (with metatables), modules (returned tables), records. Use table.create(nseq, nrec) to pre-allocate slots.

Metatables and metamethods: Customize behavior via __index, __newindex, __add, __call, __gc, __close, etc. Lua uses raw access (rawget) when querying metatables, so the metatable's own __index is not triggered during lookup.

Garbage collection: Two modes — incremental (default, marks and sweeps in small steps) and generational (collects young objects more frequently). Tune via collectgarbage("param", value) or collectgarbage("setpause"/"setstepmul"). Weak tables (__mode = "k", "v", or "kv") allow keys or values to be collected.

Coroutines: Independent threads of execution that yield explicitly via coroutine.yield(). Create with coroutine.create(f), run with coroutine.resume(co, ...), wrap into callable with coroutine.wrap(f). Check status with coroutine.status(co).

To-be-closed variables: Declare with <·*close*> annotation. The value's __close metamethod is called when the variable goes out of scope (normal exit, break, return, or error). Equivalent to try/finally for resource cleanup.

Usage Examples

Running a script:

lua script.lua arg1 arg2

Minimal Lua program:

-- hello.lua
local name = arg[1] or "world"
print("Hello, " .. name .. "!")

Table as object with metatable:

local Vector = {}
Vector.__index = Vector

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

function Vector:__add(other)
    return Vector.new(self.x + other.x, self.y + other.y)
end

local a = Vector.new(1, 2)
local b = Vector.new(3, 4)
print(a.x + b.x) -- via __add: 4

Pattern matching (Lua uses its own pattern syntax, not regex):

local str = "price: $42.50"
local price = string.match(str, "%$(%d+%.?%d*)")
print(price) -- "42.50"

To-be-closed variable for resource management:

local f = io.open("data.txt", "<·*close*>")
-- f is automatically closed when it goes out of scope
for line in f:lines() do
    print(line)
end

Embedding Lua in C (minimal):

#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>

int main(void) {
    lua_State *L = luaL_newstate();
    luaL_openlibs(L);
    luaL_dostring(L, "print('Hello from C!')");
    lua_close(L);
    return 0;
}

Compile: gcc -o embed embed.c -llua -lm

Advanced Topics

Language Reference: Types, syntax, statements, expressions, operators, metamethods, garbage collection, coroutines → Language Reference

C API: Virtual stack, C closures, registry, error handling, yielding from C, all lua_* functions → C API

Auxiliary Library: luaL_* helper functions for argument checking, library registration, chunk loading, string buffers, references → Auxiliary Library

Standard Libraries: Basic, coroutine, string (with patterns), utf8, table, math, io, os, debug, package → Standard Libraries

Build and Embedding: Building from source, installation, luaconf.h customization, embedding patterns, precompiled chunks → Build and Embedding