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Date: Tue, 5 Apr 2016 17:28:20 +0100
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To: =?UTF-8?Q?Micha=C5=82_Brzuchalski?= <michal@brzuchalski.com>
Cc: Marco Pivetta <ocramius@gmail.com>, PHP Internals List <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Final properties
From: t.carnage@gmail.com (Chris Riley)

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On 5 April 2016 at 11:57, Micha=C5=82 Brzuchalski <michal@brzuchalski.com> =
wrote:

> Hi,
>
> 2016-04-05 12:13 GMT+02:00 Marco Pivetta <ocramius@gmail.com>:
>
> > Hi,
> >
> > On 5 April 2016 at 12:06, Micha=C5=82 Brzuchalski <michal@brzuchalski.c=
om>
> > wrote:
> >
> >> Hi Marco,
> >>
> >> Ad. 1 it is posiible to redeclare in a sub-class final property as
> >> non-final, here is some gist presenting my current impl working like:
> >> https://gist.github.com/brzuchal/12ebda1efed59440a78ba43bff116728
> >>
> >
> >
> It works with public, private and protected properties.
>
>
> > Does this work for public properties as well?
> >
> >
> >> Ad. 2. `final` means class variable (like static) or class instance
> >> property can not change their reference, it is impossible to replace
> zval
> >> in such property, in my opinion `immutable` is object behavior when
> using
> >> some methods you receive newly created (cloned) object which is change=
d
> >> exactly like `DateTimeImmutable`
> >> http://php.net/manual/en/datetimeimmutable.add.php
> >>
> >
> > I am aware of what `final` means in other languages, it just seems that
> > everyone then needs to translate back and forth from `final` to
> > `immutable`. In addition to that, `final` has different meaning in
> > inheritance (re-used keyword), so this adds to the confusion for people
> > unfamiliar with the feature.
> >
> > Wiki about Final in Java
> https://www.wikiwand.com/en/Final_(Java)#/Final_variables says:
>
> # Final variables
> A final variable can only be initialized once, either via an initializer =
or
> an assignment statement. It does not need to be initialized at the point =
of
> declaration: this is called a "blank final" variable. A blank final
> instance variable of a class must be definitely assigned in every
> constructor of the class in which it is declared; similarly, a blank fina=
l
> static variable must be definitely assigned in a static initializer of th=
e
> class in which it is declared; otherwise, a compile-time error occurs in
> both cases.[6] (Note: If the variable is a reference, this means that the
> variable cannot be re-bound to reference another object. But the object
> that it references is still mutable, if it was originally mutable.)
>
> I took the name from Java and only implemented behavior like that, thats =
wy
> I used `final`.
>
>
> >> Ad. 3 it would be awesome if there could be final variables in general=
,
> >> it would be quite stable if no one could change your variable, AFAIK
> zvals
> >> have IMMUTABLE flag which could be used, don't know it for sure I'm
> rather
> >> PHP dev than C there would be need some internals guru to ask if it's
> >> posiible.
> >>
> >> P.S. We've meet on PHPCon'15 in Poland, thanks for +1.
> >>
> >
> > YW!
> >
> >
> >>
> >> Cheers,
> >> --
> >> Micha=C5=82 Brzuchalski (aka brzuchal)
> >>
> >> 2016-04-05 11:13 GMT+02:00 Marco Pivetta <ocramius@gmail.com>:
> >>
> >>> Hi Micha=C5=82,
> >>>
> >>> First of all: +1 to this: very useful for value objects!
> >>>
> >>> A few questions:
> >>>
> >>>  * can you re-declare a final property in a sub-class, making it
> >>> therefore non-final? (I have reasons to do that, related with alterin=
g
> >>> states via mappers)
> >>>  * do we want to use `final`, or `immutable` for these properties?
> >>> `final` seems to just be a confusing term here.
> >>>  * is this feature portable to variables in general? I realize that
> >>> adding metadata to ZVals has huge performance implications, but it
> would be
> >>> interesting to do that for performance improvements further down the
> line
> >>>
> >>> Cheers,
> >>>
> >>>
> >>> Marco Pivetta
> >>>
> >>> http://twitter.com/Ocramius
> >>>
> >>> http://ocramius.github.com/
> >>>
> >>> On 4 April 2016 at 19:53, Micha=C5=82 Brzuchalski <michal@brzuchalski=
.com>
> >>> wrote:
> >>>
> >>>> Hey Internals,
> >>>>
> >>>> I'm new here. I've been wondering / working on adding final properti=
es
> >>>> into
> >>>> PHP lang.
> >>>>
> >>>> This work started once I had the time to read the "Core Java for
> >>>> Impateient" by Cay S. Horstmann
> >>>> and found it very usefull to have final properties like Java.
> >>>>
> >>>> Those properties differ than `const` because they can be set at
> runtime
> >>>> -
> >>>> but only once in their lifetime.
> >>>> Such properties could be very usefull in Singletons, ValueObjects et=
c.
> >>>> impl
> >>>> like:
> >>>>
> >>>> class Money {
> >>>>     public final $amount;
> >>>>     public final $currency;
> >>>>     public function __constructor($amount, $currency) {
> >>>>         $this->amount =3D $amount;
> >>>>         $this->currency =3D $currency;
> >>>>     }
> >>>> }
> >>>>
> >>>> In above example there is even no need for getter because those
> >>>> properties
> >>>> are immutable through
> >>>> the final keyword, it means those properties cannot change their
> >>>> references
> >>>> just like in Java
> >>>> https://en.wikipedia.org/wiki/Final_(Java)
> >>>>
> >>>> I've already started some impl on own fork
> >>>>
> >>>>
> https://github.com/php/php-src/compare/master...brzuchal:final-properties
> >>>> I've got some basics in C programming, don't know yet if I can impl =
it
> >>>> complex.
> >>>>
> >>>> I was wondering if it is usefull in yours opinion or is it only my
> >>>> impression.
> >>>>
> >>>> I can provide an RFC if it sounds usefull and if I get Wiki karma
> >>>>
> >>>> Thanks
> >>>> --
> >>>> Micha=C5=82 Brzuchalski (aka brzuchal)
> >>>>
> >>>
> >>>
> >>
> > As an additional question: how will this (eventually) play with typed
> > properties? I am aware that you cannot declare a class named `final`, b=
ut
> > that may change in future, so better factor it into any possible outcom=
es
> > of the RFC.
> >
> > I don't know if it works with typed properties.
> I can provide an RFC but need Wiki Karma (or smth like that) for my accou=
nt
> (login: brzuchal) and don't know how to receive it.
>
>
> > Cheers,
> >
> > Marco Pivetta
> >
> > http://twitter.com/Ocramius
> >
> > http://ocramius.github.com/
> >
>
> Cheers,
> --
> Micha=C5=82 Brzuchalski (aka brzuchal)
>

I started a discussion on this a while back, but it fizzled due to not
having an elegant solution for the 'give me a new one of these with these
values changed' problem. I would HIGHLY suggest not using the final
keyword. If final is used as a keyword I would expect it to mean that this
property definition cannot be changed in a child class. See:
https://marc.info/?l=3Dphp-internals&m=3D144766539202647&w=3D2 Would be hap=
py to
pick this up again and help get the RFC created.

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