Re: RFC - Immutable classes

a few remarks on mutator methods: * It could be a nice way to solve the "create another one almost the same" use case. * I don't mind if $clone is an explicit parameter or magically available * what happens if I call other function/methods with this $clone before the end of the function ? * and the only downside: I have to make a method just for cloning. that means I have to call a mutator multiple times if I want to make a bunch of clone, eg: because of the last point, I think I'd like the seal the clone at then end of the block/method better, here are 2 examples to illustrate what I mean class immutable foo { private $prop = 0; public function __construct($v) {$this->prop = $v;} public function bar(obj $o) {

    $e->makeSomethingWith($this->cloneAndEdit(42));

} public function many($n) {

    $a = [];
    for ($i = 0; $i < $n; $i++) {
      $a[] = $this->cloneAndEdit($i));
    }
    return $a;

} public function mut cloneAndEdit($n) {

    $clone->prop = $n;

} } // vs class immutable foo { private $prop = 0; public function __construct($v) {$this->prop = $v;} public function bar(obj $o) {

    $c = $clone $this;
    $c->prop = 42;
    $e->makeSomethingWith($c);

} public function many($n) {

    $a = [];
    for ($i = 0; $i < $n; $i++) {

$a[] = $c = $clone $this;

      $c->prop = 42;
    }
    return $a;

} } I understand that it's still not clear exactly when the object should be sealed but if it can works this one would have my preference On 04/09/2016 14:10, Michał Brzuchalski wrote:

2016-09-04 10:55 GMT+02:00 Fleshgrinder <php@fleshgrinder.com>:

Hi Chris! On 9/3/2016 5:00 PM, Chris Riley wrote:

- Properties can be declared immutable. Immutable properties may only be changed under two circumstances: a) In the objects constructor b) If they are null (This enables setter injection if required)

The constraint b) would make the object mutable and defeat the purpose of the immutable modifier since any property could change at any time if it was NULL at the beginning. Requiring syncing in concurrent environments. On 9/3/2016 5:00 PM, Chris Riley wrote:

- Arrays assigned to immutable properties would not be possible to change

Array support would definitely be very nice. I mean, we have constant arrays already, hence, it is possible. On 9/3/2016 5:00 PM, Chris Riley wrote:

- Objects assigned to immutable properties would be possible to change,

so

long as the same object remained assigned to the property.

This would once more lead to mutability and the constraint of immutability would be violated. On 9/3/2016 5:00 PM, Chris Riley wrote:

From a developer adoption point of view, I think these two points are important to making immutable classes generally useful. Without 1, it

will

be a nuisance to use 3rd party libraries esp those which retain compatibility for PHP < 7.2. Without 2 you block the ability to use

setter

injection, which I personally would be in favour of if it meant that devs stopped using it - it wouldn't - they would simply not use immutable classes, loosing the benefits thereof.

The adoption of the feature will be halted until 7.2 is widely available in bigger projects. That is most certainly right. However, we should aim for the best, most useful, and future proof solution and not towards the one that's adopted very fast but lacks some important constraints. Having truly immutable objects is required in concurrent scenarios and such scenarios are in the future for PHP and not in the past. Regarding setter injection: I do not see the need for it at all in the context of immutable objects. In the end we are talking about value objects here and they should not have any optional dependencies. Maybe you could come up with a use case to illustrate the need? On 9/3/2016 5:00 PM, Chris Riley wrote:

Dealing with the clone issue some of my ideas since then were: - Seal/Unseal (As per Larry's suggestion) - Parameters to __clone; in this instance the clone method would be

allowed

to change properties of the object as well as the constructor. This feels like it may breach the principal of least surprise as cloning an object

no

longer guarantees an exact copy. - A new magic method __mutate($property, $newvalue) called instead of a fatal error when a property is changed. This probably lays too many traps for developers for it to be a good idea. - Implicitly returning a new object whenever a property is changed.

Similar

reservations to the above. - A new magic method __with($newInstance, $args) and a keyword with that

is

used in place of clone eg $x = $y with ($arg1, $arg2); in this instance, __with receives a clone of $y (after calling __clone) and an array

[$arg1,

$arg2] the with magic method is allowed to mutate $newInstance and must return it. This is currently my favoured solution

How does one know which property is to be mutated in the __with method? You should also not underestimate the performance hit and the branching since you only want to change the properties that changed based on the data from the passed array. I have a third proposal after giving this some more thought. Inspired by Rust's approach to mark mutation explicitly. final immutable class ValueObject {

     public $value;

     public mutator [function] withValue($clone, $value): static {
       $clone->value = $value;
     }

}

Providing mutator | mut keyword as method modifier sounds liek a good idea, althought passing $clone parameter as first additional param could break method declaration and would be misleading. Assuming mutator method is designed to return mutated clone of immutable object having $clone variable could be handled internally without breaking method declaration. Such variable could be unlocked while in mutator method and locked on return. I was thinking about additional check if such mutator returns $clone but not $this but I don't see the need of it - assuming there is no what to change in some circumstances ther would be also possible to return $this. The return type declaration self could increase readability, but should not be required, as some developers doesn't already use return types.

A mutator function always receives the mutable clone as first argument and always returns that one. Users can have a return but they must return the clone (hence the static return type declaration). $vo1 = new ValueObject(1); $vo2 = $vo1->withValue(2); Calls are of course without the clone as it is handled by the engine. There is no special branching necessary and no performance hit at all while the logic is kept in the place where it is required. -- Richard "Fleshgrinder" Fussenegger