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Date: Fri, 2 Sep 2016 16:44:25 +0200
Message-ID: <CAA69SC7V7odXcrZAB7j7d5LshmwrDYC+HwWR-sVFLZfMnouSKQ@mail.gmail.com>
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: marijic.silvio@gmail.com (=?UTF-8?Q?Silvio_Mariji=C4=87?=)

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Hi Larry,
I'm aware of that but we do have make some strong constraints there
otherwise we are undermining the strong guarantee of immutability. I would
agree to allow object modification only and only *inside* __construct() and
__clone methods. I'm trying to come up with idea how would that look like.
If you guys have some suggestions, that would be great.

2016-09-02 16:27 GMT+02:00 Larry Garfield <larry@garfieldtech.com>:

> 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.co=
m>
>>>>
>>> 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 u=
se
> 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 wort=
h
> 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;
>   }
> }
>
> 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), bu=
t
> that's the use case that would need to be addressed.
>
> --Larry Garfield
>
>
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>


--=20
Silvio Mariji=C4=87
Software Engineer
2e Systems

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