Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:81966
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain gmail.com designates 209.85.214.171 as permitted sender)
MIME-Version: 1.0
Sender: morrison.levi@gmail.com
In-Reply-To: <A6426D4F-AE4C-4079-98B7-4F343CBEBA77@ajf.me>
References: <CAF+90c9DgfkumH5ADjjykGd4t6Ude1TA70r=C7Vw40xQg3RHrw@mail.gmail.com>
	<CADNQb0Wy8nsMJ3yO1D=bXq3YW-k8-6s7_97xzAv1rNAdG0cuAg@mail.gmail.com>
	<4A36329B-F17B-4665-A84E-D8CF01F5B29A@ajf.me>
	<CAMUwpuQmj5JawUuLQ8PDRNY750qXiusHRan0o4TyimS3AvDNOw@mail.gmail.com>
	<A6426D4F-AE4C-4079-98B7-4F343CBEBA77@ajf.me>
Date: Thu, 5 Feb 2015 14:52:06 -0700
Message-ID: <CAFMT4NpGqw=0a18Sa47mtmFMwnL5e9J2s_KDd_sJCz4Ojaqv1A@mail.gmail.com>
To: Andrea Faulds <ajf@ajf.me>
Cc: Julien Pauli <jpauli@php.net>, Hannes Magnusson <hannes.magnusson@gmail.com>, 
	Nikita Popov <nikita.ppv@gmail.com>, PHP internals <internals@lists.php.net>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Subject: Re: [PHP-DEV] Allow dropping typehints during inheritance
From: levim@php.net (Levi Morrison)

On Thu, Feb 5, 2015 at 5:14 AM, Andrea Faulds <ajf@ajf.me> wrote:
> Hi Julien,
>
>> On 5 Feb 2015, at 12:10, Julien Pauli <jpauli@php.net> wrote:
>>
>> If we allow larger type, why doesn't such code work ?
>>
>> interface A { }
>> interface B extends A { }
>>
>> class C {
>>     public function foo(A $a) { }
>> }
>>
>> class D extends C {
>>     public function foo(B $a) { } // E_STRICT
>> }
>>
>> This is wrong IMO.
>
> Well, firstly that=E2=80=99s the wrong way round: inheriting classes can =
only *increase* the range of supported values, but you=E2=80=99ve done exac=
tly the opposite.
>
> But even if you fixed your code, you=E2=80=99d still have an error. This =
ispresumably because doing anything other than simple invariance causes eno=
rmous problems related to compilation order and autoloading, as we discover=
ed with the Return Types RFC.

I would hardly call them "enormous problems". Just normal problems
that I think were easier to avoid than to deal with given my schedule
and the time-frame for PHP 7.

To chime in regarding allowing contravariant parameter types: I
struggle to find use cases for it. I can only think of one use-case
and it's flawed: when something has declared an Iterator parameter and
you widen it to include Traversable. However, even though Traversable
is a parent of Iterator you can't directly call iterator methods on
it, so it could break the calling code despite the super-type check
passing.