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/dev/earth1aus5
Posted 08 January 2013 - 05:37 PM
OOP in Lua
Introduction to OOP
OOP (Object-oriented programming) is a style of computer programming that represents concepts as “objects” that have data fields (attributes that describe the object) and associated functions known as methods.
If you didn’t know that, this tutorial probably isn’t for you (this tutorial assumes at least some knowledge about OOP).
OOP in Lua
Lua does not have any OOP functionality, but one of its features – metatables – can be used to simulate OOP. A metatable in Lua is a table which describes another table (table-ception? no?)
Let’s Go!
Note: In this tutorial, I’ll be using Java terminology such as “class” and “constructor”. Just to clarify.
In this tutorial, we’ll be creating a “class” called Person, which has one field, name, three methods, getName(), setName(name) and toString(), and one constructor, new().
First off, we will define the Person “class”.
Person = {}
Person_mt = {}Now, we will define the setName, getName and toString methods.
function Person.setName(self, newName)
self.name = newName
end
function Person.getName(self)
return self.name
end
function Person.toString(self)
return "Person object. name=" .. self.name
end Now, we will define the the class constructor.
function Person.new()
local personObject = { name = "" }
setmetatable(personObject, Person_mt)
return personObject
endFinally, we need to set up the Person_mt metatable to do what we want.
Person_mt.__index = PersonAt this point (after some reshuffling), the code looks like
Person = {}
Person_mt = {}
Person_mt.__index = Person
function Person.new()
local personObject = { name = "" }
setmetatable(personObject, Person_mt)
return personObject
end
function Person.getName(self)
return self.name
end
function Person.setName(self, newName)
self.name = newName
end
function Person.toString(self)
return "Person object. name=" .. self.name
endPerson_mt.__index = Personfunction Person.new()
local personObject = { name = "" }
setmetatable(personObject, Person_mt)
return personObject
endfunction Person.getName(self)
return self.name
endThe rest of the functions should be self-explanatory.
Now for some test code!
local personObject = Person:new()
personObject:setName("John")
print(personObject:toString())Person object. name=JohnOOP Pro Tip
String objects are also defined in this way, so instead of writing string.sub(variable, 5) you can write variable:sub(5).
Thank you for reading to the end of my somewhat messy explanation. Please leave constructive criticism in the comments (replies, whatever).
