Modules: Structure

Recommended Module Structure: We discuss three commonly used Lua module structures:

1. Recommended best practice: Module with a local table interface with a return statement at the end of the module, this is the method recommended by the Lua committee.
2. Good: Module with a global table interface, this method has now been deprecated by the Lua committee.
3. Do not use: Use module(...,package.seeall) syntax, this is an older method with definite disadvantages.

1. Module with a local table interface

This is our recommended module structure.

The “advantage” of this method is that the module functions remain private (you cannot see them in the _G table). Many Lua developers prefer this since it gives tighter control over what symbols are global and which are not.

Most of the modules that we supply use this structure (though some older models use the second option).

How it works:

• Module name not exposed globally
• The module uses a local table as the interface
• Insert all functions, variables etc that you wish to expose into the interface table
• The last line of code in the module returns the interface table
• Private functions are declared as local and placed at the top of the module

Example code:

Main:

Note: this works because require() is actually just another Lua function (unlike the C/C++ #include statement, which is a preprocessor directive).

Module:

2. Module with a global table interface

This is also a good module structure, but the first method is preferred.

The “disadvantage” of this method is that the module functions are not private (you can see them in the _G table). If you prefer to make the module methods global then choose this method.

Many of the modules we supply still use this syntax, they will eventually be changed to using private interface tables.

How it works:

• Module name exposed globally
• The module uses a global table as the interface
• Insert all functions, variables etc that you wish to expose into the interface table
• Private functions are declared as local and placed at the top of the module

Example code:

Main:

Module:

There are many ways to create modules in Lua, this method is simple and reasonably private. Even though this has been deprecated, we still think it is a reasonable compromise.

3. Do no use the module(...,package.seeall) syntax

We strongly recommend that you do not use this method, it is only included for historical interest.

Using module(…,package.seeall) syntax when defining modules produces interfaces which are not pleasant to use with auto-completion in the Translator. The problem with  module(…,package.seeall) is it pulls in all the global symbols from the _G table into the module table which makes for a lot of noise showing through when using autocompletion.