02.09.2016 16:29 "Larry Garfield" <la...@garfieldtech.com> napisał(a):
>
> On 09/02/2016 09:06 AM, Silvio Marijić 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 André Rømcke <andre.rom...@ez.no>:
>>
>>>
>>>> On Sep 2, 2016, at 09:10 , Silvio Marijić <marijic.sil...@gmail.com>
>>>
>>> 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 reason
>>>
>>> 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’t it also be safe that the clone
>>> is allowed to be modified during __clone() and afterwards sealed? Like
in
>>> __construct().
>>> And if you don’t want to allow cloning, throw in __clone.
>>>
>>> Best,
>>> André
>
>
> 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 = $a;
> $this->b = $b;
> $this->c = $c;
> $this->d = $d;
> $this->e = $e;
> $this->f = $f;
> $this->g = $g;
> $this->h = $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 = 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) {
> $new = clone($this);
> $new->statusCode = $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 = $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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