classes

[stew]

hey there guys

ive just finished written a message board and an entire community based site in php. everything works fine an stuff too. anyway... the code is pretty much non-transferable to another site if i wanted to transfer it.

ive been told that using a class system of scripting can solve this problem. also ive been looking at the manual about classes, but it doesn't explain things too clearly.

i was just wondering if anyone could explain to me when you would use a class structured system and what advantages it has?

cheers

stewart

[eoghain]

First off, forget everything you just said. Making your code portable to other sites has nothing to do with classes, at least not directly. Making code portable is a matter of design and can be accomplished weather you are using Object Oriented principals (classes) or not.

That having been said classes are a nice way of building pieces of code that do 1 thing and do it well, and that can be completely self contained. So all you need to know to use a class is what API's to call, you don't have to know anything about what the class is actually doing. For example I have a database class that takes care of keeping a connection to a database. Now all I need to know when programming a database script is the API of my database class and I can forget all about the proper connection strings, error handling, query conversion, and data processing required to use a database. If for some reason I needed to have another separate connection to a database in the same script it's as easy as creating another database object and using that one when needed.

This might not be very clear, but if you want to learn about classes and object oriented programming you should get a book on it. As for your desire to make your code portable you'll need to look at the design of your code and figure out where all of the hardcoded pieces are and design a way to make those pieces easily configurable so that another site could use your code.

[saronoff]

Well its hard to say in your specific instance how the classes would be structured because that would depend slightly on your implementation. But classes allow you to create objects with defined functions. The insides of these functions can change and still everything interacts the same. In other words, if you were, on one site to have users stored in a text file and in other have them stored in a database all you would have to change is your user functions. Everything else would stay the same and call the same functions.

Basically, classes define, via their functions an interface for other code to interact with. The function never change, or shouldn't change that much, as far as name and arguments. But the actual implementation of the function can change. Therefore, you could create a function in a User class that defines a valid/invalid login and that function simply returns true if the login is valid, false otherwise. But the key is the function takes care of the actual work of logging a user in to the system. That work can change in any manner, the function still returns the same thing.

This same principles can be applied in all different areas. Something like a delete thread function, or a create thread function.

Inherently this helps portability because, with simple changes to the functions of a few classes you can change how the entire system works. However, this would also mean you would have to design your classes in such a way as to make each class a self-contained unit. That's the entire idea of classes. To create objects that can be used. For example, a car could be an object, or a bicycle each made up of other objects like steering wheel, etc.

Hope that helps!