CODEWITHSUNDEEP
phpclassvariablesdynamic
ABorrello
ABorrello

Reputation: 23

How do I access a modified parent variable within child classes in PHP

What is the best way to access dynamic parent variables from extended classes in php?

In the example below, I have simplified essentially what I am trying to do. I need to be able to access the variable '$variable' from child classes. However, $variable changes when class A is constructed, but the definition to class B and C does not change.

 class A {

 protected $variable = 'foo';
  public function __construct(){
    $this->variable = 'bar';
    echo($this->variable);
    $B = new B();                   //Returns 'bar'
  }
 }

 class B extends A {
   public function __construct(){
     echo($this->variable);         //Returns 'foo'
     $C = new C();
   }
 }

 class C extends B {
   public function __construct() {
     echo($this->variable);         //Returns 'foo'
   }
 }

 $A = new A();

I basically need $this->variable to return bar for all extended classes. After researching, the solution most recommended is to recall the __construct method for each class within the child's __construct, but that does not work in this situation because the child classes are being called from the parent class.

Can anybody lend a hand? Thanks :)

Upvotes: 1

Views: 1250

Answers (2)

theoemms
theoemms

Reputation: 68

The only way to have child classes inherit their parent's constructor set variables is to call the parent's constructor.

Maybe something like this is the answer?

class A {
 protected $variable = 'foo';
  public function __construct(){
    $this->variable = 'bar';
    echo($this->variable);
  }
  public function init(){
    $B = new B();
    //Carry on
    $B->init();
  }
 }

 class B extends A {
   public function __construct(){
     parent::__construct();
     echo($this->variable);
   }
   public function init(){
     $C = new C();
     //Carry on
   }
 }

 class C extends B {
   public function __construct() {
     parent::__construct();
     echo($this->variable);
   }
 }

 $A = new A();
 $A->init();

It's messy having two function calls. Perhaps a different design pattern is the way to go?

Upvotes: 1

Matt Browne
Matt Browne

Reputation: 12419

As @theoemms pointed out, the parent constructor is not called unless you call it explicitly with parent::__construct(). Another workaround could be to check which class is being instantiated using get_called_class() (available since PHP 5.3):

class A {

 protected $variable = 'foo';
  public function __construct(){
    $this->variable = 'bar';
    echo($this->variable);
    if (get_called_class() == 'A') {
      $B = new B();                   //Returns 'bar'
    }
  }
 }

 class B extends A {
   public function __construct(){
     parent::__construct();
     echo($this->variable);         //Returns 'bar'
     if (get_called_class() == 'B') {
       $C = new C();
     }
   }
 }

 class C extends B {
   public function __construct() {
     parent::__construct();
     echo($this->variable);         //Returns 'bar'
   }
 }

 $A = new A();

But I'm wondering, why do you need to do this? I think there might be a design flaw in your classes if you're running into this situation...

Upvotes: 1

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