PHP and multiple inheritance questions.

Stinger51

I have three classes I am developing, one for time, dates, and calendars.

But if I read the manual correctly, PHP classes do not support multiple inheritance. So the following would be illegal :

class Calendar extends Date extends Time;

But what if Calendar needs access to both the Date and Time classes? Can I then do (using my time class as the base class) something like :

class Date extends Time;
class Calendar extends Date;

Will the Calendar class now inherit, not only the methods in the Date class, but also the methods in the Time class? That should work, no?

Also, I am not sure about the "this" pointer. Lets assume I have this code :

class Date extends Time;

Now if I want the Date class (inside one of it's own functions) to access a Time function (called GetHour) which call is correct :

function FooDate()
{
$var = GetHour();
$var = $this->GetHour();
}

I'm getting inconsistent results here. To my way of thinking, $this->GetHour would be referring to a function inside of the Date class with the same name (if there was one), since "this" points to the current object (in this case, Date). But the interpreter is complaining that if I leave out the "$this->" construction that it can't find GetHour(). Can I also substitute an "explicit" call like :

$var = Time->GetHour();

And what if I actually had two different functions called GetHour, one in each class (not very good technique, I admit). How would I reference each?

Thanks in advance.

IceD

PHP doen't support multiply inheritance (BTW - I've programmed C++ last six years and NEVER used multiply inheritance 😉)

If you want to get both Time and Date in the Calendar, make:

class Calendar
{
  var $time;
  var $date;

  function Calendar()
  {
     $time = new Time();
     $date = new Date();
  }
}

This is the best solution, I think.

if you want to access method of the particular class use Class::Method syntax (Time::getHour e.g.)
Why to have two different classes for time and date??? Make one class DateTime and use it!
Inherating Calendar from Time (or Date) isn't good idea at all! Read some good OOP book!

Stinger51

Thanks. That :: syntax looks just like C++.

I haven't found any good books (as yet) about PHP classes. So I'm learning about them from scratch, trying to compare them to the way C++ and VB does things. The "functional" way I've been designing my web pages is just getting too hard to maintain.

I broke the time class file into two parts (dates and times) because it was getting overly long, about 1500 lines at last count. I figured that it would just be easier to let the date class inherit the time class and keep both modules smaller.

As far as inheritance goes, all OOP books I've read really tout the benefits of this technique. I'm not aware of any arguments against using inheritance, but I'm always willing to listen. 🙂

IceD

You can inherate e.g. Elephant from Animal class. This is good. But in your situation you should INCLUDE date into calendar, not to inhertae it calendar from day. The proper using of the inheritance and including is the most difficult topic in OOP, I think.

Stinger51

What you seem to be saying is that inheritance makes sense for animate objects, animals, airplanes, houses, etc. IOW, the base class for an airplane might be "airframe." Then we start inheriting from there, and perhaps eventually end up with an F-15. So they are building blocks of functionality.

But for inanimate ones, like time, dates, etc., it is better to perhaps just declare an object of that class where we need it, e.g. if a Date class method needs to know the current week number in the year :

function FooDate()
{
$MyTime = cTime; // declare an object of class cTime

$var = $MyTime->GetWeekNum();
}

Is this what you are getting at?

IceD

Here is another example:
1. You have Animal class and inherate Elephant from it . This is good.
2. You have Trunk, Ear, Foot classes and inherate Elephant from them. This isn't good. You should use including in this case.