variable variables + objects in fields

Question

I am trying to do something with variable variables and I got stuck on an object problem. Imagine this class setup:

class A
{
  public $field = 10;
}

class B
{
  public $a;

  public function __construct()
  {
    $this->a = new A();
  }
}

Now everyone knows that this pice of code works:

$a = new A();
$var = 'field';
echo $a->$var; // this will echo 10

Is there any possibility I could make something like this work?:

$b = new B();
$var = 'a->field';
echo $b->$var; // this fails

Note: any option which does not use eval function?

Answer 1

You can write a custom __get method on your class to access the childrens property. This works:

class A
{
  public $field = 10;
}

class B
{
  public $a;

  public function __construct()
  {
    $this->a = new A();
  }

  public function __get($property) {
    $scope = $this;

    foreach (explode('->', $property) as $child) {
      if (isset($scope->$child)) {
    $scope = $scope->$child;
      } else {
    throw new Exception('Property ' . $property . ' is not a property of this object');
      }
    }

    return $scope;
  }
}

$b = new B();
$var = 'a->field';
echo $b->$var;

Hope that helps