Classes question

semtex

I basically have 2 classes. The first one is called Visitor and contains functions for people that are not logged in. Then I have a class called User, this one contains functions for logged in users.

The class User extends the class Visitor. I have a function in class Visitor that basically performs a mysql query and returns the results. But I want that same function to be available to logged in users as well (class User), but with more options.

What's the best way to do this?

laserlight

Have the User class override that member function from Visitor.

semtex

Is that really the best way? I mean the function in the User class will basically contain the same code as the one in Visitor. So I should write the same code twice. Apart from some extra lines that would result in extra options for logged in users.

I always feel like writing the same code twice is not good coding?

NogDog

It's hard to suggest an optimal solution without knowing what the methods are doing, how they are constructed, etc. But here are a couple random thoughts to consider:

One possibility might be to break the method up into two or more methods, isolating the part that will be different into its own method (probably private). Then you would only need to overwrite that "sub-method". In the most extreme case, that private method might be empty in the Visitor class, with the main method calling it even though nothing will happen.

Another possibility might be to overwrite the method, but the bulk of it would duplicate the parent method simply by invoking it:

class User extends Visitor
{
   public function example()
   {
      parent::example();
      // additional code here...
   }
}

laserlight

One possibility might be to break the method up into two or more methods, isolating the part that will be different into its own method (probably private). Then you would only need to overwrite that "sub-method". In the most extreme case, that private method might be empty in the Visitor class, with the main method calling it even though nothing will happen.

Yeah, the template method pattern, though the "the part that will be different" would be in a protected, not private, member function otherwise it cannot be overriden.

semtex

Thanks for the insight guys and/or girls!

Shrike

You seem have two types of object which share some common functionality. In which case it would seem sensible to seperate them completely, and place the common functionality in a base, usually abstract, class. This is what the Template Method pattern describes.

Shrike

Thinking on, it would also make sense to isolate the abilities which a user has depending on their state. In which case using a Strategy may be more appropriate. Imagine you want to add some Admin user functionality. Continually using inheritance to override functionality is often a bad code smell.

semtex

What do you mean with using a "Strategy"? The Strategy pattern?

Shrike

Yes.

semtex

Okay, thanks. I guess I'll have to move on to the next step and learn those design patterns.