Why do I get "definition differs" if they are the same?

Question

In Laravel, I have a class User that extends Authenticatable and uses a trait called Activable:

class User extends Authenticable {

    use Activable;

    protected $is_active_column = 'is_active';

}

trait Activable {

    /**
     * The name of the column with the activable status
     *
     * @var string
     */
    protected $is_active_column = 'is_active';

}

When I try to find a User in tinker I get this error:

[!] Aliasing 'User' to 'App\Models\User' for this Tinker session.

PHP Fatal error:  App\Models\User and App\Traits\Activable define the same property ($is_active_column) in the composition of App\Models\User. However, the definition differs and is considered incompatible.

Answer 1

This is intended behavior. The PHP documentation on Traits is explicit about this

Properties

Traits can also define properties.

Example #12 Defining Properties

<?php
trait PropertiesTrait {
    public $x = 1;
}

class PropertiesExample {
    use PropertiesTrait;
}

$example = new PropertiesExample;
$example->x;
?>

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.

Example #13 Conflict Resolution

<?php
trait PropertiesTrait {
    public $same = true;
    public $different = false;
}

class PropertiesExample {
    use PropertiesTrait;
    public $same = true;
    public $different = true; // Fatal error
}
?>