How to Make Better Reuse of PHP Code using Traits Part 1: Basic Code Reuse

What is a Trait?

Using Multiple Traits

Conclusion

Introduction

This article assumes you have a basic understanding of the Object Model used in PHP, including inheritance, visibility, properties, methods and class abstraction. You can review these concepts in the articles Extending PHP Classes and the Object Model and Class Abstraction in PHP.

What is a Trait?

Traits are a lot like abstract classes with some differences which allow them to be used by several independent classes at the same time. When I think of Traits, I imagine a set of tools like screwdrivers. If a class wants to use them, all they have to do is ask.

trait screwDrivers {
    
    public $type;
    
    public function slottedDriver() {
        
        $this->type = 'slotted';
        
    }
    
    public function phillipsDriver() {
        
        $this->type = 'phillips';
        
    }
    
    public function starDriver() {
        
        $this->type = 'star';
        
    }
    
}

class myTools {
    
    use screwDrivers;
    
}

In the above example, the myTools class is using the trait screwDrivers. myTools, which can represent my personal toolbox, now has a set of screwdrivers in it as implemented by the trait. For the purposes of this article, the implementation is pretty basic since each method simply sets the property $type.

Traits can not be instantiated, so you cannot create an object using a trait just by itself. A class must use the traits to access the its methods. The following code instantiates the class, uses one of the traits methods and outputs the result set in the $type property, which will be slotted in this case.

$tools = new myTools();
$tools->slottedDriver();
echo $tools->type;

Using Multiple Traits

I want more than just screwdrivers in my toolbox, so I will add a set of wrenches as well.

trait screwDrivers {
    
    public $driverType;
    
    public function slottedDriver() {
        
        $this->driverType = 'slotted';
        
    }
    
    public function phillipsDriver() {
        
        $this->driverType = 'phillips';
        
    }
    
    public function starDriver() {
        
        $this->driverType = 'star';
        
    }
    
}

trait wrenches {
    
    public $wrenchType;
    
    public function openWrench() {
        
        $this->wrenchType = 'open';
        
    }
    
    public function boxWrench() {
        
        $this->wrenchType = 'box';
        
    }
    
    public function allenWrench() {
        
        $this->wrenchType = 'allen';
        
    }
    
}

class myTools {
    
    use screwDrivers, wrenches;
    
}

myTools is now using screwDrivers and wrenches. Notice that the $type property has been changed to $driverType and $wrenchType in the traits.

If a class defines a property or includes traits which define properties of the same name, an E_STRICT warning is issued. If these duplicated properties do not have the same values or types, then the script will fail with a fatal error.

To avoid this, name properties in a way to ensure they are unique. A more advanced approach is to use accessor methods, which is beyond the scope of this article.

Conclusion