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Date: Fri, 2 Sep 2016 16:46:42 +0200
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To: Larry Garfield <larry@garfieldtech.com>
Cc: PHP Internals List <internals@lists.php.net>
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Subject: Re: [PHP-DEV] RFC - Immutable classes
From: michal.brzuchalski@gmail.com (=?UTF-8?Q?Micha=C5=82_Brzuchalski?=)

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02.09.2016 16:29 "Larry Garfield" <larry@garfieldtech.com> napisa=C5=82(a):
>
> On 09/02/2016 09:06 AM, Silvio Mariji=C4=87 wrote:
>>
>> Well at the moment expection is thrown in case when you try to clone
>> immutable object. But you do seem to have valid point there regarding
>> __clone method. I'm definitely going to give it a thought.
>>
>> Best,
>> Silvio.
>>
>> 2016-09-02 15:52 GMT+02:00 Andr=C3=A9 R=C3=B8mcke <andre.romcke@ez.no>:
>>
>>>
>>>> On Sep 2, 2016, at 09:10 , Silvio Mariji=C4=87 <marijic.silvio@gmail.c=
om>
>>>
>>> wrote:
>>>>
>>>> Hi Fleshgrinder,
>>>>
>>>> Since Michal answered most of the questions, I'll just add some notes.
>>>> Initially I added restrictions to abstract classes, but I did think
about
>>>> that over the last couple of days and couldn't find any concrete reaso=
n
>>>
>>> for
>>>>
>>>> that restriction, so I think I'm going to remove that. As far as
cloning,
>>>> it is disabled for immutable objects, because you'll end up with the
copy
>>>> of object that you can not modify. I did mention in Cons sections that
>>>> cloning is disabled, maybe it should be made more clear.
>>>
>>>
>>> _If_ there are use-cases for it, wouldn=E2=80=99t it also be safe that =
the clone
>>> is allowed to be modified during __clone() and afterwards sealed? Like
in
>>> __construct().
>>> And if you don=E2=80=99t want to allow cloning, throw in __clone.
>>>
>>> Best,
>>> Andr=C3=A9
>
>
> I'd have to agree here.  I love the idea of "lockable" immutable
objects.  However, the __clone() method has to be a modifiable area just
like __construct() or else it's effectively useless for anything more than
a trivial object.
>
> This was one of the main concerns with immutability in the PSR-7
discussions.  Consider this sample class, with 8 properties (entirely
reasonable for a complex value object):
>
> immutable class Record {
>   public $a;
>   public $b;
>   public $c;
>   public $d;
>   public $e;
>   public $f;
>   public $g;
>   public $h;
>
>   public function __construct($a, $b, $c, $d, $e, $f, $g, $h) {
>     $this->a =3D $a;
>     $this->b =3D $b;
>     $this->c =3D $c;
>     $this->d =3D $d;
>     $this->e =3D $e;
>     $this->f =3D $f;
>     $this->g =3D $g;
>     $this->h =3D $h;
>   }
> }
>
> Now I want a new value object that is the same, except that $d is
incremented by 2.  That is, I'm building up the value object over time
rather than knowing everything at construct time.  (This is exactly the use
case of PSR-7.)  I have to do this:
>
> $r1 =3D new Record(1, 2, 3, 4, 5, 6, 7, 8);
>
> $r2 - new Record($r1->a, $r1->b, $r1->c, $r1->d + 2, $1->e, $r1->f,
$r1->g, $r1->h);
>
> That's crazy clunky, and makes immutable objects not very useful. Imagine
a money object where you had to dissect it to its primitives, tweak one,
and then repackage it just to add a dollar figure to it.  That's not worth
the benefit of being immutable.
>
> The way PSR-7 addressed that (using fake-immutability, basically), was
this:
>
> class Response {
>   // ...
>
>   protected $statusCode;
>
>   public function withStatusCode($code) {
>     $new =3D clone($this);
>     $new->statusCode =3D $code;
>     return $new;
>   }
> }
>

I see only way in somehow invoking closere with cloning. That'll need
additional syntax. Clone is left side operator not a function - it's not
being called with parenthesis. If this was an object method accessible from
public it coud gace such closure injected...

> That is, outside of the object there's no way to modify it in place, but
it becomes super easy to get a slightly-modified version of the object:
>
> $r2 =3D $r1->withStatusCode(418);
>
> And because of PHP's copy-on-write support, it's actually surprisingly
cheap.
>
> For language-level immutable objects, we would need some equivalent of
that behavior.  I'm not sure exactly what form it should take (explicit
lock/unlock commands is all I can think of off hand, which I dislike), but
that's the use case that would need to be addressed.
>
> --Larry Garfield
>
>
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