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To: "'Julien Pauli'" <jpauli@php.net>,
	"'Andrea Faulds'" <ajf@ajf.me>
Cc: "'Hannes Magnusson'" <hannes.magnusson@gmail.com>,
	"'Nikita Popov'" <nikita.ppv@gmail.com>,
	"'PHP internals'" <internals@lists.php.net>
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Date: Thu, 5 Feb 2015 13:16:29 +0100
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Subject: AW: [PHP-DEV] Allow dropping typehints during inheritance
From: php@tutteli.ch ("Robert Stoll")


> -----Urspr=C3=BCngliche Nachricht-----
> Von: julienpauli@gmail.com [mailto:julienpauli@gmail.com] Im Auftrag =
von Julien Pauli
> Gesendet: Donnerstag, 5. Februar 2015 13:10
> An: Andrea Faulds
> Cc: Hannes Magnusson; Nikita Popov; PHP internals
> Betreff: Re: [PHP-DEV] Allow dropping typehints during inheritance
>=20
> On Thu, Feb 5, 2015 at 2:08 AM, Andrea Faulds <ajf@ajf.me> wrote:
>=20
> > Hi Hannes,
> >
> > > On 4 Feb 2015, at 23:58, Hannes Magnusson
> > > <hannes.magnusson@gmail.com>
> > wrote:
> > >
> > > So what it supports "more inputs"?
> > > It does constitute an LSP violation. "more inputs" is not what the
> > > guarantee is at all, if that is what you want you'd typehint on a
> > > interface.
> > >
> > >
> > > It is a LSP failure to allow a string, or any other scalar value,
> > > when the parent requires a specific type/object.
> > >
> > > It sucks that we fail our arginfo very frequently, but this is the
> > > way
> > it is :]
> >
> > An interface requires only a minimum standard for accepted input. If =
a
> > class implementing that interface allows a wider range of values, =
but
> > still allows at least what the interface requires it to, it is not =
an
> > LSP violation. Scalars are not special.
> >
>=20
> If we allow larger type, why doesn't such code work ?
>=20
> interface A { }
> interface B extends A { }
>=20
> class C {
>     public function foo(A $a) { }
> }
>=20
> class D extends C {
>     public function foo(B $a) { } // E_STRICT }
>=20
> This is wrong IMO.
>=20
>=20
> Julien.P

Because this would be covariance and violates LSP. Considering the =
following:

function foo(C $c){
   $c->foo(new A);
}

if you substitute C with D then suddenly the code would not work =
anymore.

Cheers,
Robert