CODEWITHSUNDEEP
phpoopinheritancetraits
Sjors Ottjes
Sjors Ottjes

Reputation: 1217

Why can you override the initial value of a property defined in a trait that is used in a parent class?

The PHP docs says the following about overriding trait properties:

If a trait defines a property then a class can not define a property with the same name unless it is compatible (same visibility and initial value), otherwise a fatal error is issued.

However, when you use a trait in an abstract class, then you can override the properties defined in the trait in a class extending that abstract class:

<?php

trait PropertyTrait
{
    public $prop = 'default';   
}

abstract class A
{
    use PropertyTrait;
}

class B extends A
{
    public $prop = 'overridden';

    public function write()
    {
        echo $this->prop;       
    }
}

$b = new B();

$b->write(); // outputs "overridden"

Live demo

The code above works, but I can't find any reference about it in the documentation. Is this an intended feature?

Upvotes: 1

Views: 610

Answers (1)

yivi
yivi

Reputation: 47359

Because for all intents and purposes B is not using PropertyTrait. That's used by A to compose the abstract class.

B has no visibility of what traits A is using. If you were to execute class_uses on B, you'd get an empty array. Docs, and example.

Since B is not using any traits, the class is free to override any inherited properties.

The fact that A is an abstract class has no bearing on this. The same behaviour would happen with any class that extended a class that was composed using traits.

Upvotes: 3

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