Tutorial on Class function visibility (that public/protected/private dilemma)

Dev Shed Forums Sponsor:

May 18th, 2012, 01:57 AM

FlyingBeetroot

Contributing User

Join Date: May 2012

Posts: 73

Time spent in forums: 20 h 24 m 52 sec
Reputation Power: 35

Tutorial on Class function visibility (that public/protected/private dilemma)

You can check out it here at flying beetroot

Understanding OO Visibility - PHP

Enjoy!

May 18th, 2012, 06:35 PM

E-Oreo

Lost in code

Dev Shed God 7th Plane (8000 - 8499 posts)

Join Date: Dec 2004

Posts: 8,054

Folding Points: 945 Folding Title: Novice Folder

Time spent in forums: 2 Months 1 Day 5 h 27 m 59 sec
Reputation Power: 7104

Your tutorial is well written and does a good job of explaining those concepts.

Just because I'm OCD and my life revolves around PHP I'm going to point out two things:

(1) A constructor actually doesn't need to be public. In fact, there is a particular use-case where you would not want the constructor to be public:

PHP Code:


		
			
class special_class

    {

        public static function factory_method()

        {

            return new self;

        }

        protected function __construct()

        {

            echo "constructed";

        }

    }

    $inst = special_class::factory_method();

Declaring the constructor as protected in this case prevents me from bypassing the factory method.

(2) You can actually call a protected or private method from an instantiation inside the class that contains the functions. In fact, the instantiation doesn't even need to be inside the class containing the functions. A protected or private method can be called on any object from any context that has visibility of those methods. Meaning that even something like this is legal syntax:

PHP Code:


		
			
class special_class_a

    {

        public function pub($arg)

        {

            $arg->pro();

        }

        protected function pro()

        {

            echo "pro-a";

        }

    }

    

    class special_class_b extends special_class_a

    {

        protected function pro()

        {

            echo "pro-b";

        }

    }

    

    $inst1 = new special_class_a;

    $inst2 = new special_class_b;

    

    $inst1->pub($inst2);

Comments on this post

FlyingBeetroot agrees: Thanks mate - I'll update accordingly

__________________
PHP FAQ
How to program a basic, secure login system using PHP
Connect with me on LinkedIn

Quote:

Originally Posted by Spad

Ah USB, the only rectangular connector where you have to make 3 attempts before you get it the right way around

May 19th, 2012, 03:13 AM

FlyingBeetroot

Contributing User

Join Date: May 2012

Posts: 73

Time spent in forums: 20 h 24 m 52 sec
Reputation Power: 35

Thanks mate - I did know about the factory idea; but all the code I've seen uses die() in the public constructor to prevent standard instantiation.

As for point 2 - valid argument (in fact I wrote a router class for URL parsing that does this) - but it's slightly different in nature to the example I gave. Nonetheless; given it is around the same lines; I will update my tutorial to include this exception.

Cheers for taking the time to read it though

Greatly appreciated.

May 19th, 2012, 04:08 AM

FlyingBeetroot

Contributing User

Join Date: May 2012

Posts: 73

Time spent in forums: 20 h 24 m 52 sec
Reputation Power: 35

OK, it's updated and I think with your comments incorporated it's a lot better. Thanks again.

May 19th, 2012, 10:43 AM

E-Oreo

Lost in code

Join Date: Dec 2004

Posts: 8,054

Time spent in forums: 2 Months 1 Day 5 h 27 m 59 sec
Reputation Power: 7104

Quote:

As for point 2 - valid argument (in fact I wrote a router class for URL parsing that does this) - but it's slightly different in nature to the example I gave. Nonetheless; given it is around the same lines; I will update my tutorial to include this exception.

Ah, actually my example using extension was meant to show a "most complicated" situation. It works with other cases too, such as passing an instance of special_class_a to pub() or constructing an instance of "self" inside pub instead of using the argument. At least under PHP 5.3, the tutorial's example of self instantiation executes correctly with no errors.

However, this is sort of an edge case as objects are rarely used in this way.

Tutorial on Class function visibility (that public/protected/private dilemma)

Developer Shed Advertisers and Affiliates