phparchitect-2019-08

38 \ August 2019 \ http://www.phparch.com

Generated Singletons

Internal Apparatus

No Return Type

Listing 2, class CarleyStatePark, is identical to Listing 1

except that getInstance() does not specify a return type.

Does the generated code change? Yes, it does. The getIn-

stance() return sequence is shorter. We don’t see the

VERIFY_RETURN_TYPE V6 instruction. Now we know how, or at

least where, the PHP virtual machine implements the func-

tion/method return type. The VERIFY_RETURN_TYPE instruction

handles that task.

Here is the fragment of generated code for CarleyStatePark.

It returns self::$instance as before, but does not check the

return type:

L12 (17): EXT_STMT

L13 (17): V6 = FETCH_STATIC_PROP_R string("instance") (self)

(exception)

L14 (17): RETURN V6

Remove Duplication
We now have two nearly-identical classes, CamdenState-
Park and CarleyStatePark. Let’s remove code duplication by
creating a parent class. CamdenStatePark and CarleyStatePark
will extend that parent class. This is a mistake, but we don’t
know that yet, so let’s keep going! See Listing 3.
Here are the modified child classes, Listing 4 and Listing 5.
We added require_once 'StatePark.php'; so the code gener-
ator can find the parent class. Note that we add the @method
annotation to each child class, so our editor can help us keep
the object types correct (see line 8 of Listing 4 and Listing 5).

Listing 3. Class StatePark

1. <?php


2. declare(strict_types=1);


3. 
   


4. namespace App\GeneratedSingleton;


5. 
   


6. abstract class StatePark {


7. /* @var StatePark /


8. private static $instance;


9. 
   


10. private function __construct() {


11. }


12. 
    


13. public static function getInstance(): self {


14. if (!self::$instance) {


15. self::$instance = new static;


16. }


17. return self::$instance;


18. }


19. 
    


20. }

Listing 4. Modified class CamdenStatePark

1. <?php


2. declare(strict_types=1);


3. 
   


4. namespace App\GeneratedSingleton;


5. require_once 'StatePark.php';


6. 
   


7. /**


8. 
   
   
   
   • @method static getInstance() : CamdenStatePark
   
   
   
   


9. */


10. class CamdenStatePark extends StatePark {


11. }

Listing 5. Modified class CarleyStatePark

1. <?php


2. declare(strict_types=1);


3. 
   


4. namespace App\GeneratedSingleton;


5. require_once 'StatePark.php';


6. 
   


7. /**


8. 
   
   
   
   • @method static getInstance() : CarleyStatePark
   
   
   
   


9. */


10. class CarleyStatePark extends StatePark {


11. }

Listing 2. Class CarleyStatePark

1. <?php


2. declare(strict_types=1);


3. 
   


4. namespace App\GeneratedSingleton;


5. 
   


6. class CarleyStatePark {


7. /* @var CarleyStatePark /


8. private static $instance;


9. 
   


10. private function __construct() {


11. }


12. 
    


13. public static function getInstance() {


14. if (!self::$instance) {


15. self::$instance = new self;


16. }


17. return self::$instance;


18. }


19. }