2.9 – Environments

Besides metatables, objects of types thread, function, and userdata have another table associated with them, called their environment. Like metatables, environments are regular tables and multiple objects can share the same environment.

Threads are created sharing the environment of the creating thread. Userdata and C functions are created sharing the environment of the creating C function. Non-nested Lua functions (created by loadfile, loadstring or load) are created sharing the environment of the creating thread. Nested Lua functions are created sharing the environment of the creating Lua function.

Environments associated with userdata have no meaning for Lua. It is only a convenience feature for programmers to associate a table to a userdata.

Environments associated with threads are called global environments. They are used as the default environment for threads and non-nested Lua functions created by the thread and can be directly accessed by C code (see §3.3).

The environment associated with a C function can be directly accessed by C code (see §3.3). It is used as the default environment for other C functions and userdata created by the function.

Environments associated with Lua functions are used to resolve all accesses to global variables within the function (see §2.3). They are used as the default environment for nested Lua functions created by the function.

You can change the environment of a Lua function or the running thread by calling setfenv. You can get the environment of a Lua function or the running thread by calling getfenv. To manipulate the environment of other objects (userdata, C functions, other threads) you must use the C API.