In this tutorial I'll be covering a very important concept in Lua: metatables. Knowledge of how to use metatables will allow you to be much more powerful in your use of Lua. Every table can have a metatable attached to it. A metatable is a table which, with some certain keys set, can change the behaviour of the table it's attached to. Let's see an example.
t = {} -- our normal table
mt = {} -- our metatable, which contains nothing right now
setmetatable(t, mt) -- sets mt to be t's metatable
getmetatable(t) -- this will return mt
As you can see, getmetatable
and setmetatable
are the main functions here; I think it's pretty obvious what they do. Of course, in this case we could contract the first three lines into this:
Lua is the most flexible language I've ever used, aside from its speed, this is probably the best thing about it. In this post, I'm going to show you how to specify names of things in function arguments, without strings. The method I'll use it a bit hackish, and isn't fit for normal operation; but hey, Lua allows us do it!
For an example, say you had an OOP implementation that used a function called class
like this:
class('MyClass')
What we're going to change that into, is this:
Read moreWhen I create a class in Lua, there are always times when I need to use a getter or setter on attributes, instead of raw access. The way I've always done this is to use methods with names like getFoo
and setFoo
. And then to keep my API consistent, I have to switch every single property to use these getter/setter methods. The pain about these type of methods is that:
obj.foo
and obj.foo = v
.What I really wanted was syntax like this:
Read moreI've recently created an experimental Lua object-orientation library using the closure approach to OOP. It's based largely on MiddleClass, sharing a lot of design features with it.
I've already written a README, so go and visit the GitHub repo for more information.
The technique I'm about to present, may seem obvious, but I'll share it anyway. The way I would create mixins that inherit stuff from other mixins is this:
Mixin = {}
function Mixin:included(class)
if not includes(ParentMixin, class) then
class:include(ParentMixin)
end
end
When the mixin is included, it will check whether the class includes the mixin, and if not, it will include it, therefore simulating inheritance. It's good to check if the class includes the parent mixin, because MiddleClass does not do this itself.
Read moreI thought I'd demonstrate a method for making a singleton class in MiddleClass. If you don't know, MiddleClass is an object-orientation library for Lua.
So why would you want to make a class that only has one instance with MiddleClass? Couldn't you just use a table? Well, making it a class in MiddleClass allows you to take advantage of a number of other cool things that MiddleClass has on offer, like mixins, inheritance and so on. So let's have a look at the method.
Read more