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Date: Thu, 27 Nov 2014 20:19:22 +0100
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Subject: Re: [PHP-DEV] Idea: immutable class / object
From: dev@mabe.berlin (Marc Bennewitz)

Thoughts ?

Am 25.11.2014 um 22:26 schrieb Marc Bennewitz:
> Hi internals,
>
> In OOP it's a sometimes a common issue to know the state of an object 
> and to know if it was changed respectively it it can change state.
>
> We already have such objects like DateTImeImmutable and new proposed 
> objects like UString also introduce immutable objects.
>
> I think it would be really helpful to see this kind of issue addressed 
> in a standardized way:
>
> if you approve with this I would write down a more structured RFC.
>
> Now see the following code snipped:
>
> <?php
>
> immutable class MyImmutableClass {
>     public static $staticProperty = 'private static';
>     public $ts;
>     public $obj;
>
>     public function __construct($obj = null) {
>         $this->ts = time();
>         $this->setObj($obj);
>     }
>
>     public function getTimestamp() { return $this->ts; }
>     public function getObj() { return $this->obj; }
>     public function setObj($obj) { $this->obj = $obj; }
> }
>
> // initialize
> $obj = new DateTImeImmutable();
> $obj = new MyImmutableClass($obj);
>
> // check if immutable
> var_dump(MyImmutableClass::immutable);
> var_dump($obj::immutable);
>
> // read properties
> var_dump($obj->ts, $obj->obj);
> var_dump($obj->getTimestamp(), $obj->getObj());
>
> // ERROR: Immutable objects can not contain mutable properties
> $obj = new MyImmutableClass(new stdClass);
>
> // ERROR: Immutable objects can not be changed after initialization
> $obj = new MyImmutableClass();
> $obj->setObj($obj);
> $obj->obj = $obj;
>
> // ERROR: It's not allowed to change immutable variables
> MyImmutableClass::$staticProperty = 'new value';
>
> ?>
>
> Because of for immutable objects it's not allowed to set an mutable 
> object as property
> you can be sure the object's state will be consistent. That's the main 
> difference from
> marking all properties readonly or similar functionalities.
>
> Additionally it's simple to test if an class/object is immutable and 
> document it for free.
>
> Downside: New Keyword "immutable"
>