Maxi Contieri

Posted on Nov 29, 2020 • Updated on Dec 19, 2021 • Originally published at maximilianocontieri.com

Code Smell 37 - Protected Attributes

#oop #webdev #tutorial #codenewbie

Protected attributes are great for encapsulating and controlling access to our properties. They might be warning us for another smell.

Problems

Sub classification for code reuse purposes.
Liskov substitution violation (SOLID principle).
Possible subclass overrides.

Solutions

Favor composition
Don't subclassify attributes.
Extract behavior to separate objects.
Use [traits](https://en.wikipedia.org/wiki/Trait_(computer_programming) (if available).

Wrong

<?

abstract class ElectronicDevice {

    protected $battery;

    public function __construct(OperatingSystem $battery) {
        $this->battery = $battery;
    }

}

abstract class Idevice extends ElectronicDevice {

    protected $operatingSystem;

    public function __construct(Battery $battery, OperatingSystem $ios) {
        $this->operatingSystem = $ios;
        parent::__construct($battery)
  }

}

final class Ipad extends Idevice {

    public function __construct(Battery $battery, OperatingSystem $ios) {
        parent::__construct($battery, $ios)
  }

}

final class Iphone extends Idevice {

    private $phoneModule:

  public __construct(Battery $batery, OperatingSystem $ios, PhoneModule $phoneModule) {
    $this->phoneModule = $phoneModule;
    parent::__construct($battery, $ios)
  }

}

Right

<?

interface ElectronicDevice {
    //...
}

interface PhoneCommunication {
    //...
}

final class Ipad implements ElectronicDevice {

    private $operatingSystem;
    private $battery;

    public function __construct(Battery $battery, OperatingSystem $ios) {
        $this->operatingSystem = $ios;
        $this->battery = $battery;
    }
}

final class Iphone implements ElectronicDevice, PhoneCommunication {

    private $phoneModule;
    private $operatingSystem;
    private $battery;

    public function __construct(Battery $battery, OperatingSystem $ios, PhoneModule $phoneModule) {
        $this->phoneModule = $phoneModule;
        $this->operatingSystem = $ios;
        $this->battery = $battery;
    }
}

Detection

In languages supporting protected attributes we can avoid them by policy or have a warning of this smell.

Conclusion

Protected attributes are yet another tool we should use carefully. Every decision is a smell, and we should be very careful with attributes and inheritance.

Relations

Code Smell 11 - Subclassification for Code Reuse

Maxi Contieri ・ Oct 30 '20 ・ 2 min read

#oop #codenewbie #tutorial

More Info

Traits on Wikipedia

Credits

Photo by Jonathan Farber on Unsplash

Subclasses shouldn’t always share all characteristics of their parent class but will do so with inheritance. This can make a program’s design less flexible. It also introduces the possibility of calling methods on subclasses that don’t make sense or that cause errors because the methods don’t apply to the subclass.

Steve Klabnik