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Date: Mon, 15 Oct 2012 18:33:18 +0200
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To: Clint Priest <cpriest@zerocue.com>
Cc: Levi Morrison <morrison.levi@gmail.com>, 
	"internals@lists.php.net" <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [PHP-DEV [RFC] Property Accessors v1.2 : Interfaces
From: colder@php.net (Etienne Kneuss)

Hi,

On Mon, Oct 15, 2012 at 6:02 PM, Clint Priest <cpriest@zerocue.com> wrote:
> Because fundamentally interfaces are designed to explain a way of communi=
cating and properties are symmetrical and non-observable.
>
> The implementing class cannot "know" when a property has changed.

Do you agree that there is nothing that distinguishes

class A {
    public $v;
}

from

class B {
   private $_v;
   public $v { get { return $this->v; }; set($n) { $this->v =3D $n; }}
}

when it comes to a client of B reading and writing to $b->v ? That's
the entire point of accessors: being able to seamlessly intercept
usages of properties with custom code.

If you define an interface saying interface A { public $v { get;set;}
} you are only saying to the user: objects of type A will have a
property $v that you can read and write to.
Whether it is a set of accessors or a property belongs to the
implementation detail of the class implementing A, the user should not
be able to see a difference when interacting with the class, as he
will do it through $obj->v and $obj->v =3D ...;

I can understand why we might not want that in PHP in order to
simplify the implementation, but it we follow logical reasoning I
can't see why we shouldn't implement that.


This discussion makes we wonder about another aspect of the patch that
is unclear:

class A {
   public $v =3D 2;
}

class B extends A {
   public $v { get { .. }; set { .. } };
}

Will $b->v trigger the accessors, will it ignore them and access "v"
in the properties table, or is overriding existing properties using
accessors rejected during compilation?

Best,

>
> -Clint
>
> On Oct 15, 2012, at 9:37 AM, "Levi Morrison" <morrison.levi@gmail.com> wr=
ote:
>
>>> I *think* we are on the same page here, though I'm not sure what 'user'=
 is referring to (user of interface "implementer") or (user of class B).  I=
n any case, I don't believe that your class B would be allowed at present, =
but if it is, then it should not be allowed because defining a property to =
satisfy the requirements of an accessor is not right.
>>
>> According to whom?  In my opinion, not allowing a property to satisfy
>> the requirement of an accessor is wrong.



--=20
Etienne Kneuss
http://www.colder.ch