OOP nightmare / "visibility"

[jeffrydell]

I'm new to OOP. Last week was momentous as I got my first class to
actually do something.

Might as well admit this right up front, I am by no means "sold" on
the way OOP php works.

That said, here's WHY I'm not very excited about jumping further in
the OOpool:

(This is pseudo-code, I HIGHLY doubt the error is a matter of syntax.)

index.php:

require_once(a.class.php)
require_once(b.class.php)
require_once(c.class.php)

$a = new class A()

......

moving on to code in class A:

$b = new class B() ... which contains a 'helper method' to return
values from within this class
$c = new class C() ... which contains a reference to one of class B's
helper methods.

Both Class B and Class C 'extend' Class A

Class C throws these messages regarding the line with a reference to
$B->helperMethod()

Notice: Undefined variable: (Name of Class 😎 in /path/to/Class/C.php
on line 10

Fatal error: Call to a member function helperMethod() on a non-object
in /path/to/Class/C.php on line 10

I thought the whole idea behind OOP was to write small, reusable code
that would 'play well with others' and pass info around so that a
change in one place could affect necessary changes in another object's
state. AND so that one object could 'ask' another for information by
way of a getMethod().

So why is it so blinking difficult to get one class "see" another,
much less access the data in another?

That asked, I guess the more relevant question is how does one code so
that the Helper Method in class B() is actually available to be called
in class C?

Thanks in advance for any guidance you can offer.

[NogDog]

It may well be that I'm missing something, but if class B and C are each a "child" class of A, then their objects (B's and C's, that is) would not "share" anything other than any methods and/or class variables inherited from the "parent" class A (and only those that were not defined as "private" in A). Any new variables or methods or overwritten methods would be local only to their objects, not to their siblings' objects. If you want C to directly access a B object's methods, you would probably have to either instantiate a copy of B within C, or else pass it to C, perhaps as part of the constructor:

class C extends A
{
   private $b;

   public __construct(B $b)
   {
      $this->b = $b;
   }

   public function test()
   {
      $this->b->some_method_from_B();
   }
}

$b = new B();
$c = new C($b);
$c->test();

[NogDog]

PS: Depending on what precisely these objects are supposed to be doing, it might make more sense to have C extend B (which in turn extends A).

[jeffrydell]

NogDog;10911705 wrote:

PS: Depending on what precisely these objects are supposed to be doing, it might make more sense to have C extend B (which in turn extends A).

Thanks for the earlier reply - yes, you hit it on the head ... didn't miss anything. I'll have to 'pass it' though rather than extending (I think).

Let me see if I have this right. Multiple classes can extend the same 'parent', but one class cannot extend multiple 'parent' objects. Is that correct?

[laserlight]

jeffrydell wrote:

Let me see if I have this right. Multiple classes can extend the same 'parent', but one class cannot extend multiple 'parent' objects. Is that correct?

Yes, PHP does not support multiple inheritance. However, it does support implementing multiple interface constructs.

[jeffrydell]

Thanks - this is the reason I cannot use C extends B in the example above. C actually needs to extend D (which has not yet been discussed), but needs to have access to the properties within B.

So I have set this up as NogDog suggests (passing B to C when instantiating), and already 'see' the data needed.

Your willingness to help out at a very basic level is greatly appreciated!