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Date: Mon, 14 Nov 2016 09:20:23 +0000
Message-ID: <CAKiSzdARmkeWphdF8xnYyrQfN6sQRX_M1PebF3yQ54bXgJOrLg@mail.gmail.com>
To: =?UTF-8?Q?Micha=C5=82_Brzuchalski?= <michal@brzuchalski.com>, 
	Joe Watkins <pthreads@pthreads.org>
Cc: Levi Morrison <levim@php.net>, Niklas Keller <me@kelunik.com>, 
	"Christoph M. Becker" <cmbecker69@gmx.de>, PHP Internals List <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=089e01183e0e1e48b205413f5a16
Subject: Re: [PHP-DEV] [RFC][VOTE] Object typehint
From: joshdifabio@gmail.com (Josh Di Fabio)

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Content-Type: text/plain; charset=UTF-8
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On Mon, Nov 14, 2016 at 8:54 AM Micha=C5=82 Brzuchalski <michal@brzuchalski=
.com>
wrote:

> Hi All,
>
> Id' like to anounce voting reset - will end in two weeks on 28.11.2016 at
> midnight and requires 2/3 majority as previously.
>
> There were improvements suggested by Joe Watkins and earlier by Nikita
> Popov to the patch.
>
> Those improvements are described on RFC under "Covariance" section
> https://wiki.php.net/rfc/object-typehint#covariance

This section describes covariance of method arguments. Is this a mistake?
Should this be contravariance? Covariant arguments go against LSP.

>
> It means any `object` typehint or return type can be narrowed to more
> specified type (class name) similar to `iterable` pseudo-type but behaves
> covariant (more general type can be raplaced with narrowed one).
>
> P.S. I hope this improvement will bring more positive votes.
>
> regards,
> --
> Micha=C5=82
>
> 2016-11-10 13:30 GMT+01:00 Joe Watkins <pthreads@pthreads.org>:
>
> > Levi,
> >
> >     You are assuming it would *need* to be removed :)
> >
> >     Future RFC's must deal with the engine as they find it, as this RFC
> > has done.
> >
> >     If it is true that this would prohibit enums being non-objects, and
> > I'm not certain that it does, then enums would have to be objects, if
> > that's how they find the engine.
> >
> >     If your only concern is about a non-existent feature, then maybe
> > you're concern can be alleviated by the non-existent JIT (which does
> > partially exist): With a JIT, it doesn't much matter what represents
> enums
> > anyway.
> >
> >     These are problems for the future, not today.
> >
> > Cheers
> > Joe
> >
> > On Thu, Nov 10, 2016 at 12:20 PM, Levi Morrison <levim@php.net> wrote:
> >
> >> 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,
> >> variance
> >> >> >> > 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 som=
e
> >> >> >> practical use cases for covariance of a method with return type
> >> object,
> >> >> >> but I don't see how contravariance could be achieved for
> parameters
> >> of
> >> >> >> 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 al=
l
> >> other
> >> >> > 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 wee=
ks
> >> 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 guarante=
e
> >> >> 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.
> >>
> >
> >
>
>
> --
> regards / pozdrawiam,
> --
> Micha=C5=82 Brzuchalski
> about.me/brzuchal
> brzuchalski.com


P.S. Apologies for the non-plaintext email.

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