Mastering the Nmap Scripting Engine

Metatables and metamethods

Metamethods allow us to change the behavior of a table by writing custom functions for operators—such as comparing objects, arithmetical operations, and more. For example, let's say we would like to overload the "add" functionality of our table object with a new function that adds certain fields we select. Normally, the addition operation isn't valid on tables but, with metatables, we can overwrite the __add metamethod to perform whatever we need.

Arithmetic metamethods

The metamethods supported by Lua tables are as follows:

Metamethod	Description
__add	Addition operator
__mul	Multiplication operator
__sub	Subtraction operator
__div	Division operator
__unm	Negation operator
__pow	Exponentiation operator