1.1.4. Mutate object after instantion

The Container supports objects to be mutated after it is constructed. This is especially useful when you have separate container configs that both need to define the object that will be constructed. Use cases could be adding routes to a router from multiple configs or adding commands to a console application object.

After the Container constructs a new instance of an object, you can specify which other objects will mutate the original object before locking the container.

Say we have classes like the following:

namespace Vendor\Package;

use Aura\Di\Injection\MutationInterface;

class Example
{
    protected $foo;

    public function setFoo($foo)
    {
        $this->foo = $foo;
    }
}

class ExampleMutation implements MutationInterface
{
    public function __invoke(object $object): object
    {
        $object->setFoo('mutated');
        return $object;
    }
}

We can specify that it should be mutated after construction. We can instantiate the mutation directly or lazy.

$di->mutations['Vendor\Package\Example'][] = new ExampleMutation(); // direct
$di->mutations['Vendor\Package\Example'][] = $di->lazyNew(ExampleMutation::class); // lazy

Just like with any other class, you inject params to the mutation class.

class ExampleMutation implements MutationInterface
{
    private $argX, $argxY;
    
    public function __construct ($argX, $argY) {
        $this->argX = $argX;
        $this->argY = $argy;
    }
    
    public function __invoke(object $object): object
    {
        $object->setFoo($this->argX);
        $object->setBaz($this->argY);
        return $object;
    }
}

$di->params[ExampleMutation::class]['argX'] = $di->lazyGet('service');
$di->params[ExampleMutation::class]['argY'] = $di;
$di->mutations['Vendor\Package\Example'][] = $di->lazyNew(ExampleMutation::class);

When the mutation calls methods on an immutable object, you can return the new object.

class RegisterRoutesMutation implements MutationInterface
{
    public function __invoke(object $object): object
    {
        $object = $object->withRoute(new Vendor\Router\Route('/contact', 'abc'));
        $object = $object->withRoute(new Vendor\Router\Route('/hello_world', 'xyz'));
        return $object;
    }
}

N.b.: If you try to access $di->mutations after calling newInstance() (or after locking the Container using the lock() method) the Container will throw an exception. This is to prevent modifying the params after objects have been created. Thus, be sure to set up all mutations for all objects before creating an object.