Re: RFC - Immutable classes

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 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.romcke@ez.no>: >> >> >>> On Sep 2, 2016, at 09:10 , Silvio Marijić <marijic.silvio@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; > } > } > > 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 > > > -- > PHP Internals - PHP Runtime Development Mailing List > To unsubscribe, visit: http://www.php.net/unsub.php > > -- Silvio Marijić Software Engineer 2e Systems