Programming in Lua : 2.7

This first edition was written for Lua 5.0. While still largely relevant for Lua 5.1, there are some differences.
The second edition targets Lua 5.1 and is available at Amazon and as an e-book.
By buying the book, you also help to support the Lua project.

Programming in Lua

Part I. The Language Chapter 2. Types and Values

2.7 – Userdata and Threads

The userdata type allows arbitrary C data to be stored in Lua variables. It has no predefined operations in Lua, except assignment and equality test. Userdata are used to represent new types created by an application program or a library written in C; for instance, the standard I/O library uses them to represent files. We will discuss more about userdata later, when we get to the C API.

We will explain the thread type in Chapter 9, where we discuss coroutines.