This first edition was written for Lua 5.0. While still largely relevant for later versions, there are some differences.
The third edition targets Lua 5.2 and is available at Amazon and other bookstores.
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|Programming in Lua|
|Part II. Tables and Objects Chapter 16. Object-Oriented Programming|
A particular case of the previous approach for OO programming occurs when an object has a single method. In such cases, we do not need to create an interface table; instead, we can return this single method as the object representation. If this sounds a little weird, it is worth remembering Section 7.1, where we saw how to construct iterator functions that keep state as closures. An iterator that keeps state is nothing more than a single-method object.
Another interesting case of single-method objects occurs when this single-method is actually a dispatch method that performs different tasks based on a distinguished argument. A possible implementation for such object is as follows:
function newObject (value) return function (action, v) if action == "get" then return value elseif action == "set" then value = v else error("invalid action") end end endIts use is straightforward:
d = newObject(0) print(d("get")) --> 0 d("set", 10) print(d("get")) --> 10
This unconventional implementation for objects is quite effective.
is only two characters longer than
the more conventional
Each object uses one single closure,
which is cheaper than one table.
There is no inheritance, but we have full privacy:
The only way to access an object state is through its sole method.
Tcl/Tk uses a similar approach for its widgets. The name of a widget in Tk denotes a function (a widget command) that can perform all kinds of operations over the widget.
|Copyright © 2003–2004 Roberto Ierusalimschy. All rights reserved.|