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Date: Tue, 29 Jun 2021 09:14:33 +0200
Message-ID: <CAOWwgpnvX=1f-zzCpOPzu8az3cfiu_vD-Ez0=o8jT=KpfzbHTw@mail.gmail.com>
To: Larry Garfield <larry@garfieldtech.com>, Nikita Popov <nikita.ppv@gmail.com>
Cc: php internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="0000000000007226b605c5e25cac"
Subject: Re: [PHP-DEV] Re: [RFC] Readonly properties
From: nicolas.grekas+php@gmail.com (Nicolas Grekas)

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>
> Le lun. 28 juin 2021 =C3=A0 18:22, Larry Garfield <larry@garfieldtech.com=
> a
>> =C3=A9crit :
>>
>>> On Mon, Jun 28, 2021, at 11:17 AM, Nicolas Grekas wrote:
>>> > > > I'd like to open the discussion on readonly properties:
>>> > > > https://wiki.php.net/rfc/readonly_properties_v2
>>> > > >
>>> > > > This proposal is similar to the
>>> > > > https://wiki.php.net/rfc/write_once_properties RFC that has been
>>> > > declined
>>> > > > previously. One significant difference is that the new RFC limits
>>> the
>>> > > scope
>>> > > > of initializing assignments. I think a key mistake of the previou=
s
>>> RFC
>>> > > was
>>> > > > the confusing "write-once" framing, which is both technically
>>> correct and
>>> > > > quite irrelevant.
>>> > > >
>>> > > > Please see the rationale section (
>>> > > > https://wiki.php.net/rfc/readonly_properties_v2#rationale) for
>>> how this
>>> > > > proposal relates to other RFCs and alternatives.
>>> > > >
>>> > >
>>> > > I plan to open voting on this RFC soon. I don't think there's
>>> anything
>>> > > technical left to address here, the discussion mostly comes down to
>>> a value
>>> > > judgement. I think everyone has made their position regarding that
>>> clear...
>>> > >
>>> >
>>> > Actually, we talked off the list about a way to possibly make this wo=
rk
>>> > with __clone():
>>> >
>>> > We could allow __clone to have one argument, the object being cloned.
>>> And
>>> > when the signature declares this argument, then all readonly properti=
es
>>> > would be set as uninitialized on $this.
>>> >
>>> > A typical __clone function would look like this with readonly
>>> properties:
>>> > function __clone(object $original)
>>> > {
>>> >     $this->readonlyProp =3D clone $original->readonlyProp;
>>> > }
>>> >
>>> > That would turn my vote into a +1 if that could be made to work!
>>>
>>> That sounds like it would support deep cloning, but not with-er
>>> methods.  There's no way to provide a changed value.  It also would mea=
n a
>>> lot of work on larger objects to transfer across all the properties.  I
>>> don't really see what this would add.
>>>
>>
>> Can you elaborate about the lack of support for withers? Having some wor=
k
>> to do doesn't look like an issue to me, especially when there is no
>> alternative to compare that too.
>>
>
> I sent that too fast, I agree about withers... :)
> I'm looking for a way to +1 that RFC...
> Any other idea?
>

And I was too fast agreeing that my proposal to pass the original object as
argument was incompatible with withers.

I also think that not being compatible with deep cloning is a major issue.
Past trivial cases, the use cases I can think of where I would use readonly
require deep cloning. See eg the Symfony Request object where query params,
headers, and a few others expose state as public objects.

Here is some code that just works with them:
class C
{
    public readonly string $foo;
    public readonly string $bar;

    private $skipWhenCloning;

    public function withFoo($foo)
    {
        $this->skipWhenCloning =3D 'foo';
        $clone =3D clone $this;
        $clone->foo =3D $foo;
    }

    public function withBar($bar)
    {
        $this->skipWhenCloning =3D 'bar';
        $clone =3D clone $this;
        $clone->bar =3D $bar;
    }

    public function __clone(self $original)
    {
        foreach ($this as $k =3D> $v) {
            if ($k !=3D=3D $this->skipWhenCloning) {
                $this->$k =3D $original->$k;
            }
        }
        $this->skipWhenCloning =3D $original->skipWhenCloning =3D null;
    }
}

You might not like the boilerplate, but that just works.

Can this be considered Nikita?

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