Immutable objects and the builder pattern.

immutable.php

<?php

interface ImmutableObject {
    public function getMandatory();
    public function getOptional();
}

interface ImmutableObjectBuilder {

    public function setOptional($optional);
    
    /**
     * @return ImmutableObject
     */
    public function build($mandatory);
}

class MyObject implements ImmutableObject {
    private $mandatory;
    private $optional;

    public function __construct($mandatory) { $this->mandatory = $mandatory; }

    public function getMandatory() { return $this->mandatory; }

    public function getOptional() { return $this->optional; }
    public function setOptional() { $this->optional = $optional; }
}

class MyObjectBuilder {
    private $optional;

    public function setOptional() { $this->optional = $optional; }
    
    /**
     * @return ImmutableObject
     */
    public function build($mandatory)
    {
         $object = new MyObject($mandatory);
         if ($this->optional) {
             $object->setOptional($this->optional);
         }
         return $object;
    }
}

modify-builder.php

<?php

interface ImmutableObjectBuilder {
 
    public function setOptional($optional);
    
    /**
     * @return ImmutableObject
     */
    public function build($mandatory);
    
    /**
     * @return ImmutableObject
     */
    public function modify(ImmutableObject $object);
}
 
class MyObjectBuilder {
    private $optional;
 
    public function setOptional() { $this->optional = $optional; }
    
    /**
     * @return ImmutableObject
     */
    public function build($mandatory)
    {
         return $this->modify(new MyObject($mandatory));
    }
    
    /**
     * @return ImmutableObject
     */
    public function modify(ImmutableObject $object)
    {
         if ($this->optional) {
             $object->setOptional($this->optional);
         }
         return $object;
    }
}

use-case.php

<?php

class MyObjectService
{
    private $converter;

    /**
     * @var \ImmutableObjectBuilder
     */
    private $builder;

    /**
     * @return \ImmutableObject
     */
    public function load($id)
    {
        $dataObject = $this->repository->find($id);

        return $this->converter->toDomain($dataObject);
    }

    public function modify(\ImmutableObject $object, $optional)
    {
        // Some domain rule checks on $optional
        $this->builder->setOptional($optional);

        $object = $this->builder->modify($object);

        $this->repository->persist($this->converter->fromDomain($object));

        return $object;
    }
}