This first edition was written for Lua 5.0. While still largely relevant for later versions, there are some differences.
The fourth edition targets Lua 5.3 and is available at Amazon and other bookstores.
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Programming in Lua |  |
| Part II. Tables and Objects Chapter 13. Metatables and Metamethods |
__newindex MetamethodThe __newindex metamethod does for table updates what
__index does for table accesses.
When you assign a value to an absent index in a table,
the interpreter looks for a __newindex metamethod:
If there is one, the interpreter calls it
instead of making the assignment.
Like __index, if the metamethod is a table,
the interpreter does the assignment in that table,
instead of in the original one.
Moreover, there is a raw function that
allows you to bypass the metamethod:
The call rawset(t, k, v) sets the value v in key k
of table t without invoking any metamethod.
The combined use of __index and __newindex metamethods
allows several powerful constructs in Lua,
from read-only tables to tables with default values to
inheritance for object-oriented programming.
In the rest of this chapter we see some of these uses.
Object-oriented programming has its own chapter.
| Copyright © 2003–2004 Roberto Ierusalimschy. All rights reserved. | |