PHP Traits overwrite variable

Question

Assuming I have this trait:

trait MyTrait{

    protected static $_statVar = 'defaultStaticVal';
    protected $_var = 'defaultVal';

}

And a class that uses it

class MyClass{

    use MyTrait;

}

How would I go about changing the default values, like

use MyTrait{

    MyTrait::$_statVar = 'nonDefaultStaticVal';
    MyTrait->_var = 'nonDefaultVal';

}

I know that the shown syntax is incorrect, and also that currently, it is not allowed to change inherited trait values simply by changin them. What choices/alternatives does that leave me with?

Answer 1

PHP extend class & trait booting control

I created a small helper that solves most situations and expand your execution priorities on the class + trait booting process. The numbers used on the following example respect order of setting. Similar to the Laravel booting mechanism.

A helper class:

class TraitHelper
{
    // The helper will call the boot function on every used trait.
    static public function bootUsedTraits($obj)
    {
        $usedTraits = class_uses($obj);
        foreach ($usedTraits as $traitClass) {
        $path = explode('\\', $traitClass);
        $traitBootMethod = array_pop($path);
        $traitBootMethod = 'boot'.$traitBootMethod;
        if (method_exists($obj, $traitBootMethod)) {
            $obj->$traitBootMethod();
            }
        }
    }
}

Your class:

class MyClass{

    use MyTrait;

    // Class default values
    static protected $a = 1;
    protected $b = 2;

    function __construct()
    {
        // Class setting values before trait
        self::$a = 4;
        $this->b = 5;

        $this->traitVar = 6;


        // Trait setting values
        \TraitHelper::bootUsedTraits($this);


        // Class setting values after trait
        self::$a = 10;
        $this->b = 11;

        $this->traitVar = 12;
    }
}

Your trait:

trait MyTrait {

    // Trait default values
    protected $traitVar = 3;

    // Called on "bootUsedTraits"
    public function bootMyTrait() {
        self::$a = 7;
        $this->b = 8;

        $this->traitVar = 9;
    }
}