Lua: Tables

Lua
Basics
About Syntax Datatypes Hello World
Intermediate
Using Metatables Writing files Basic Object-orientation example Vararg statements MMF Interface
Advanced
Iterators How to take over Eastern Europe Basic Object engine
XLua
MMF Interface WIN Interface OpenGL C Libraries
Add to this template

This article assumes the use of Lua 5.1. Information may not be accurate or may need revision if you are using a different version.

This article or section is in need of expansion. Please add further information.

Tables are the only real complex data structure provided in Lua. Tables are basically arrays, specifically associative arrays, associating a key with a corresponding value. Unlike most languages, Lua's tables start at 1 instead of 0. Lua tables can store every other data type, and even mixed types. The following is a valid table:

table1 = {
    key = "test", -- defines 'key' and assigns 'test' to it 
    [3] = 5, -- assigns '5' to index 3
    ["what"] = true,
    table2 = { }, -- creates a subtable in this table 
    testfunc = function(arg) return 10 end, -- this way of defining functions must be used in tables 
    not_here = nil, -- this value does not exist
    [0] = "skipped", -- allowed but more or less ignored by default functions
}

Values in tables can be accessed in a few ways. One way is via dot syntax: table1.key will return test. Another is by specifying an integer index: table1[3] will return 5, not true, as 5 was explicitly stored in '[3]'. Strings can also used within square brackets: table1["what"] is exactly the same as table1.what, but does allow you to evaluate a string within the brackets.

Functions inside tables can called in various ways; remember, they are variables, after all. table1.testfunc(arg) and table1["testfunc"](arg) are two valid ways to call a function. Functions are also able to use colon syntax, which effectively gives Lua OO capabilities. table1:testfunc(arg) is the same as table1.testfunc(table1, arg).

Metatables are normal Lua tables that can be "attached" to other tables. They allow you to define otherwise undefined behavior: normally, adding two tables would result in an error. However, metatables allow you to define exactly how tables should be added, which would make adding tables a valid operation.