Is it possible to partially implement a class?

linchat


class a
{
     function public test { print $a; }
     function public test2 { print $b; }
}

class b extends a
{
}

What I would like to do is to hide say make "test" protected in class b, so it is only usable by class b, but "test2" would remain public.

Maybe another class say "c" could extend a but everything would be public.

laserlight

You should be able do this by declaring test as protected in class b and then have it call the parent version of test. However, you should not do this as whatever is public in the parent class should remain public in the child class.

linchat

and then have it call the parent version of test.

Not sure what you mean?

class a
{
     function protected test { print $a; }
     function public test2 { print $b; }
}

class b extends a
{
     public function test()
    {
          parent::test();
    }
}

Like that? It is a good and sadly for me, obvious solution. Is this the best/only way to do this?

laserlight

linchat wrote:
Like that?

That does not look like what you set out to do. Notice that in your original post, both a::test and a::test2 are public, but now a::test is protected. (It should also be a syntax error, anyway.)

linchat wrote:
Is this the best/only way to do this?

Assuming that you are talking about your original post, I was going to rant about how this violates the Liskov substitution principle, but it turns out that I need not waste my breath: PHP itself prevents you from creating the horror that you want to inflict. Sorry, but it is time for you to change your wants.

As a proof of concept, try running this script and read the error message:

<?php

class A {
    public function test() {}
    public function test2() {}
}

class B extends A {
    protected function test() {}
}

linchat

I know, based on your code, that cannot be done. Maybe I am not explaining myself properly.

Basically, I want to extend a class, now, I do not want all of the public methods from the parent class to be available as public to the child class, I want some of the parent class methods to become protected in the child class.

My reasoning, I have an object for specific use, my child object ALSO has specific use but is dependent on the parent. Just looking to shed those unnecessary methods from the parent (from public view) in the child for the sake of clarity.

Ex.
I have an object the reads data.
I have an object that writes data.

The object that writes data is dependent on the read object to function. But many of the methods in the read object I do not want exposed to the public in the write object, just for the sake of clarity.

class A {
    public function test() {}
    public function test2() {}
}

class B extends A {
    protected function test() {}
}

laserlight

linchat wrote:
Basically, I want to extend a class, now, I do not want all of the public methods from the parent class to be available as public to the child class, I want some of the parent class methods to become protected in the child class.

What you want violates the Liskov substitution principle.

linchat wrote:
My reasoning, I have an object for specific use, my child object ALSO has specific use but is dependent on the parent. Just looking to shed those unnecessary methods from the parent (from public view) in the child for the sake of clarity.

All the non-private methods from the parent are necessary in the child. There is no such thing as unnecessary non-private methods.

linchat wrote:
Ex.
I have an object the reads data.
I have an object that writes data.

The object that writes data is dependent on the read object to function. But many of the methods in the read object I do not want exposed to the public in the write object, just for the sake of clarity.

Yes, and thus you should not use inheritance. If you do use inheritance, then these two reader/writer classes should inherit from a common base class that would probably be an abstract base class.

linchat

Ok, thanks. After reading your posts, I went back and recoded. Think I was trying to take the hard way around the simple path... It happens... 🙂