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Metatables allow us to change the behavior of a table. For instance, using metatables, we can define how Lua computes the expression a+b, where a and b are tables. Whenever Lua tries to add two tables, it checks whether either of them has a metatable and whether that metatable has an __add field. If Lua finds this field, it calls the corresponding value (the so-called metamethod, which should be a function) to compute the sum.
<!-- Taken from the Lua PIL (http://www.lua.org/pil/13.html) --~~~~ -->
== Setting and getting a metatable ==

You will use setMetatable and getMetatable to set and get metatables.

You use getMetatable(table) to get your metatable from a table. It will return the __metatable metafield
in the table.

setMetatable(table, metatable) to set your table's metatable. It will error if the __metatable metafield
is set.

However, if the table has a metatable with the metafield __metatable, it will error when you use setMetatable and return what it is set to when getMetatable is called.

== Metamethods ==

A metamethod is a type of function which changes the default way a table acts. The table below demonstrates what each
one is called, and how each one is used. <br/>

{| class="wikitable"
|-
| Name || Description || Arguments passed
|-
| __index
| Used when table[variable] is called.
| The variable.
|-
| __newindex
| Used like __index, but it is only called when the variable matches an empty space in the table.
| The variable.
|-
| __call
| A metamethod to turn a table's name into a function, or whatever you want it to do.
| Function, Tuple
|-
| __metatable
| Used for protecting metatables, called when getmetatable() is used on the table, setmetatable() just errors.
| Nothing (as far as Unit158 knows)
|-
| __mul
| Used as an operator overloader for multiplication.
| The two objects being "multiplied".
|-
| __div
| Used as an operator overloader for division.
| The two objects being "divided".
|-
| __sub
| Used as an operator overloader for substraction.
| The two objects being "subtracted".
|-
| __add
| Used as an operator overloader for addition.
| The two objects being "added".
|-
| __mod
| Used as an operator overloader for modulo.
| The two objects being "divided".
|-
| __pow
| Used as an operator overloader for exponentiation operation.
| The two objects being exponentiated.
|-
| __unm
| I am not exactly sure how this one works, it is for negatives though.
| The table being changed into a negative. <!-- Feel free to change this one X] -->
|-
| __eq
| __eq is an operator overloader for comparison.
| The two objects being compared
|-
| __lt
| Less than.
| The two objects being compared
|-
| __le
| Less than or equal to.
| The objects being compared
|-
| __concat
| The objects being concatenated
| The two objects being concatenated
|-
| __len
| The # operator.
| The object having the operation performed on it.
|-
|}

== Examples ==
{{Example
|desc=Use __eq to check if two tables are equal
|code=table1 = {x=0, y=1, z=0}
 table2 = {x=1, y=1, z=0}
 metatable = {__eq = function(operand1, operand2, type)
 if operand1.x == operand2.x and operand1.y == operand2.y and operand1.z then --Note: In reality you might want to first check if your these variables actually exist
     return true
 else
     return false
 end }
 setmetatable(table1, metatable)
 setmetatable(table2, metatable)
 if table1 == table2 then
     print("Equal")
 else
     print("Not equal")
 end
}}
== External links ==
* [http://www.lua.org/manual/5.1/manual.html#2.8 Lua 5.1 Reference Manual: Metatables]

[[Category:Tutorials]]