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Date: Thu, 10 Nov 2016 05:20:56 -0700
Message-ID: <CAFMT4Npz8qncXAFBPitU87=DOC-3v+DQcGxdzoHN3oQUmbyK8w@mail.gmail.com>
To: Joe Watkins <pthreads@pthreads.org>
Cc: Niklas Keller <me@kelunik.com>, "Christoph M. Becker" <cmbecker69@gmx.de>, 
	=?UTF-8?Q?Micha=C5=82_Brzuchalski?= <michal@brzuchalski.com>, 
	PHP Internals List <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC][VOTE] Object typehint
From: levim@php.net (Levi Morrison)

On Thu, Nov 10, 2016 at 5:18 AM, Joe Watkins <pthreads@pthreads.org> wrote:
> Morning Levi,
>
>> There is a future compatibility issue of this same type with `object`:
>
> If that is an issue, it is for future RFC's to deal with.
>
> Cheers
> Joe
>
>
> On Thu, Nov 10, 2016 at 12:12 PM, Levi Morrison <levim@php.net> wrote:
>>
>> On Thu, Nov 10, 2016 at 2:11 AM, Niklas Keller <me@kelunik.com> wrote:
>> > 2016-11-09 21:53 GMT+01:00 Christoph M. Becker <cmbecker69@gmx.de>:
>> >
>> >> On 09.11.2016 at 17:28, Joe Watkins wrote:
>> >>
>> >> >     I want to explain why I voted no on this:
>> >> >
>> >> >     I think it's significantly less useful without variance, varian=
ce
>> >> > is
>> >> > something that is usually difficult to achieve in PHP, but not for
>> >> > this
>> >> > feature in particular.
>> >>
>> >> Can you please elaborate what you mean with variance?  I see some
>> >> practical use cases for covariance of a method with return type objec=
t,
>> >> but I don't see how contravariance could be achieved for parameters o=
f
>> >> type object.
>> >>
>> >> If your suggestion is only about invariance of object return types, I=
'm
>> >> not sure if this very special case would make sense (for consistency
>> >> reasons).
>> >>
>> >
>> > We already have it for iterable -> array. We would have it for all oth=
er
>> > types if there wouldn't be an implementation issue.
>> >
>> > Regards, Niklas
>> >
>> > Cheers,
>> >> Christoph
>> >>
>> >> >     I absolutely want it, but I want it to be properly useful.
>> >> >
>> >> >     If the RFC were halted and patched to include variance, I'd +1
>> >> > it.
>> >> >
>> >> > Cheers
>> >> > Joe
>> >> >
>> >> > On Sun, Nov 6, 2016 at 5:28 PM, Micha=C5=82 Brzuchalski
>> >> > <michal@brzuchalski.
>> >> .com>
>> >> > wrote:
>> >> >
>> >> >> Hi everyone,
>> >> >>
>> >> >> Two weeks have passed since this RFC was put to discussion here.
>> >> >>
>> >> >> Therefore, I'm going to put it to a vote for inclusion in PHP 7.2.
>> >> >>
>> >> >> Voting starts today, 2016-11-06, and will close after two weeks on
>> >> >> the
>> >> >> Sunday 2016-11-20 at midnight.
>> >> >>
>> >> >> The RFC and voting widget can be found here:
>> >> >> https://wiki.php.net/rfc/object-typehint
>> >> >>
>> >> >> It's a normal 2/3 majority required vote.
>> >> >>
>> >> >> Thanks!
>> >> >> --
>> >> >> regards / pozdrawiam,
>> >> >> --
>> >> >> Micha=C5=82 Brzuchalski
>> >> >> about.me/brzuchal
>> >> >> brzuchalski.com
>> >> >>
>> >> >
>> >>
>> >>
>> >> --
>> >> PHP Internals - PHP Runtime Development Mailing List
>> >> To unsubscribe, visit: http://www.php.net/unsub.php
>> >>
>> >>
>>
>> In a return type context `iterable` can be changed to `Traversable` or
>> `array`; it cannot be changed to `Collection` as we cannot guarantee
>> at compile-time that `Collection` implements Traversable.
>>
>> There is a future compatibility issue of this same type with `object`:
>> right now the only user-definable types are objects. However, enums
>> are an often requested feature and they may not be objects. Thus we
>> wouldn't be able to guarantee that `Foo` is an object. There is a
>> draft RFC with a patch for enums and expect it will come to a
>> discussion soon, so I don't think we'll have to wait very long to know
>> the answer here.
>
>

I strongly disagree here; once we add `object` return type covariance
it cannot easily be removed.