Immutable object and CQS

immutable_object_and_cqs.php

<?php

class SomeImmutableObject {
    
    private $a;
    private $b;
    
    public function __construct($a, $b) {
        $this->a = $a;
        $this->b = $b;
    }
    
    public function withA($a) {
        $cloned = clone $this;
        $cloned->a = $a;
        
        return $cloned;
    }
    
}

class SomeClassThatWantToChangeAInImmutableObject {
    
    private $eventDispatcher;
    
    public function __construct($eventDispatcher) {
        $this->eventDispatcher = $eventDispatcher;
    }
    
    public function someCommand($immutableObject, $a) {
        $newImmutableObject = $immutableObject->withA($a);
        
        $this->eventDispatcher->dispatch(new NewImmutableObjectWasCreated($newImmutableObject));
    }
    
}

class SomeClass {
    
    private $eventListener;
    private $someClassThatWantToChangeAInImmutableObject;
    
    public function __construct($eventListener, $someClassThatWantToChangeAInImmutableObject) {
        $this->eventListener = $eventListener;
        $this->someClassThatWantToChangeAInImmutableObject = $someClassThatWantToChangeAInImmutableObject;
    }
    
    public function doSomethingWithImmutableObject($immutableObject) {
        $thisNewImmutableObjectWillBeCreated = null;
        $this->eventListener->addListener(
            NewImmutableObjectWasCreated::class, 
            function ($event) use ($thisNewImmutableObjectWillBeCreated) {
                $thisNewImmutableObjectWillBeCreated = $event->getNewImmutableObject();
            }
        );
        
        $this->someClassThatWantToChangeAInImmutableObject->someCommand($immutableObject, 555);
        
        // Do something with "new immutable object" that has been created during "some command"
    }
    
}