# Fix for #53727 (is_subclass_of resolution with interfaces)

- Thread: https://externals.io/message/53674
- Original archive: https://news-web.php.net/php.internals/53674
- Started by Ralph Schindler on 2011-06-29T19:39:46+00:00
- Messages: 17
- Reply by email to internals@lists.php.net
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## #53674 — Ralph Schindler — 2011-06-29T19:39:46+00:00

URL: https://externals.io/message/53674#53674

Hi all,

Concerning: https://bugs.php.net/bug.php?id=53727

I had put together a quick patch against PHP_5_3 to fix, for what I and 
others might consider, an issue with `is_subclass_of()` returning false in 
this situation:

   interface A {}
   class B implements A {}
   var_dump(is_subclass_of('B', 'A')); // false, should be true

It returns false in situations where a class does not have a parent.  If 
a parent currently exists, the above works fine.  For example:

   interface A {}
   class B implements A {}
   class C extends B {}
   var_dump(is_subclass_of('B', 'A')); // true

Attached is a patch against PHP_5_3, I can create a patch against 
PHP_5_4 if need be.

I've added a test file and all the current Zend/tests run as expected.

Thanks,
Ralph

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## #53675 — david.zuelke@bitextender.com — 2011-06-29T19:42:46+00:00

URL: https://externals.io/message/53674#53675 · In reply to: #53674

>  interface A {}
>  class B implements A {}
>  class C extends B {}
>  var_dump(is_subclass_of('B', 'A')); // true

Typo there; that should be 'C', not 'B'.

David

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## #53677 — Paul Dragoonis — 2011-06-29T20:20:18+00:00

URL: https://externals.io/message/53674#53677

> Correct.
>
> I was hasty in that example, the first was copied & tested (and is reflected
> in the test, as is that variation of what I wrote up.)
>
> Either way, test and patch work in 5_3.

Doesn't this functionality confuse matters?

If this patch is added, is there now no difference between instanceof
and `is_subclass_of()`. If this is the case my question is then why do
we have two methods to do the same thing?

I thought instanceof was for parent classes + interfaces.. and
 `is_subclass_of()` was just for parent classes.

Regards,
Paul Dragoonis.

>
> Thanks,
> -ralph
>
> 
> > […]

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## #53678 — david.zuelke@bitextender.com — 2011-06-29T20:22:54+00:00

URL: https://externals.io/message/53674#53678 · In reply to: #53677

> 
> > […]
> 
> Doesn't this functionality confuse matters?
> 
> If this patch is added, is there now no difference between instanceof
> and `is_subclass_of()`. If this is the case my question is then why do
> we have two methods to do the same thing?
> 
> I thought instanceof was for parent classes + interfaces.. and
> `is_subclass_of()` was just for parent classes.

instanceof is a language construct and only operates on object instances.

David

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## #53679 — Paul Dragoonis — 2011-06-29T20:25:58+00:00

URL: https://externals.io/message/53674#53679 · In reply to: #53678

On Wed, Jun 29, 2011 at 9:22 PM, David Zülke
<david.zuelke@bitextender.com> wrote:
> 
>
> > […]
>
> instanceof is a language construct and only operates on object instances.
>

I didn't spot you could pass a string into `is_subclass_of()` I thought
it was only objects. With that in mind it would be good to have
subclass_of() include interfaces.


> David

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## #53680 — Benjamin Eberlei — 2011-06-29T21:00:52+00:00

URL: https://externals.io/message/53674#53680 · In reply to: #53678

On Wed, 29 Jun 2011 22:22:54 +0200
David Zülke <david.zuelke@bitextender.com> wrote:

> 
> 
> > […]
> 
> instanceof is a language construct and only operates on object instances.
> 
> David
> 
> 

plus there is a difference if $a is a User is_subclass_of($a, 'User') returns false, $a instanceof User returns true.

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## #53681 — Martin Scotta — 2011-06-29T21:05:49+00:00

URL: https://externals.io/message/53674#53681 · In reply to: #53679

> On Wed, Jun 29, 2011 at 9:22 PM, David Zülke
> <david.zuelke@bitextender.com> wrote:
> > […]
> wrote:
> > […]
> reflected
> > […]
>
> I didn't spot you could pass a string into `is_subclass_of()` I thought
> it was only objects. With that in mind it would be good to have
> subclass_of() include interfaces.
>
>
are you kidding, right?

$class = 'stdClass';
$instance = new $class;
var_dump( $instance instanceof $class );



>
> > […]

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## #53682 — david.zuelke@bitextender.com — 2011-06-29T21:10:33+00:00

URL: https://externals.io/message/53674#53682 · In reply to: #53681

> are you kidding, right?
> 
> $class = 'stdClass';
> $instance = new $class;
> var_dump( $instance instanceof $class );

That still only works on instances. Not on class names. Which this dicussion is about.

David

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## #53683 — Anthony Ferrara — 2011-06-29T21:12:59+00:00

URL: https://externals.io/message/53674#53683 · In reply to: #53681

> are you kidding, right?

var_dump('Foo' instanceof 'Bar');

//Fatal Error: instanceof expects an object instance, constant given


> 
>
> > […]
> are you kidding, right?
>
> $class = 'stdClass';
> $instance = new $class;
> var_dump( $instance instanceof $class );
>
>
>
> > […]

---

## #53691 — Matt Pelmear — 2011-06-30T01:13:24+00:00

URL: https://externals.io/message/53674#53691

Seems odd to me that is_subclass_of returns true for interfaces... I never
realized that before.

Personally I would prefer a separate method to check for interfaces, since
they aren't really classes (at least in my head), but I suppose that would
break BC. (I've always wanted a method for checking if a class implements an
interface.)
So, maybe this patch makes sense to me, and some additional method for
checking only interfaces would be nice? (I can't think of a good name for
such a method.) Thoughts?

-Matt

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## #53692 — David Muir — 2011-06-30T04:44:48+00:00

URL: https://externals.io/message/53674#53692 · In reply to: #53691

> Seems odd to me that is_subclass_of returns true for interfaces... I never
> realized that before.
>
> Personally I would prefer a separate method to check for interfaces, since
> they aren't really classes (at least in my head), but I suppose that would
> break BC. (I've always wanted a method for checking if a class implements an
> interface.)
> So, maybe this patch makes sense to me, and some additional method for
> checking only interfaces would be nice? (I can't think of a good name for
> such a method.) Thoughts?
>
> -Matt
> 
>

As in `class_implements()` (shown in Ralph's example)?

David

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## #53693 — Matt Pelmear — 2011-06-30T05:01:24+00:00

URL: https://externals.io/message/53674#53693 · In reply to: #53692

Not like `class_implements()`, since that requires processing the returned
array... Rather something that would function similarly to `is_subclass_of()`
(in that it returns a bool, not an array), but for interfaces.
I seem to run into a need for that on a fairly regular basis. (when I first
found `class_implements()` this is what I thought it did before reading the
docs)

-matt

> 
> > […]
never
> > […]
since
> > […]
would
> > […]
an
> > […]
>
> As in `class_implements()` (shown in Ralph's example)?
>
> David

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## #53695 — David Muir — 2011-06-30T05:11:16+00:00

URL: https://externals.io/message/53674#53695 · In reply to: #53693

> Not like `class_implements()`, since that requires processing the returned
> array... Rather something that would function similarly to `is_subclass_of()`
> (in that it returns a bool, not an array), but for interfaces.
> I seem to run into a need for that on a fairly regular basis. (when I first
> found `class_implements()` this is what I thought it did before reading the
> docs)
>
> -matt

Oops. My bad. Missed the `array_key_exists()` part in the example.

David

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## #53697 — Dmitry Stogov — 2011-06-30T07:39:55+00:00

URL: https://externals.io/message/53674#53697 · In reply to: #53674

Hi Ralph,

I agree with expected behavior, but didn't understand the patch and 
which side effects it may have as well as the original implementation of 
is_a_impl(). It looks for me like one huge bug :)

Please reassign the bug to me, if you like me to take a deeper look.
I can do it only on next week.

Thanks. Dmitry.


> Hi all,
>
> Concerning: https://bugs.php.net/bug.php?id=53727
>
> I had put together a quick patch against PHP_5_3 to fix, for what I and
> others might consider, an issue with `is_subclass_of()` returning false in
> this situation:
>
> interface A {}
> class B implements A {}
> var_dump(is_subclass_of('B', 'A')); // false, should be true
>
> It returns false in situations where a class does not have a parent. If
> a parent currently exists, the above works fine. For example:
>
> interface A {}
> class B implements A {}
> class C extends B {}
> var_dump(is_subclass_of('B', 'A')); // true
>
> Attached is a patch against PHP_5_3, I can create a patch against
> PHP_5_4 if need be.
>
> I've added a test file and all the current Zend/tests run as expected.
>
> Thanks,
> Ralph

---

## #53711 — Ralph Schindler — 2011-06-30T22:48:49+00:00

URL: https://externals.io/message/53674#53711 · In reply to: #53697

Hey Dmitry,

is_a_impl() is an implementation that is shared by `is_a()` and 
 `is_subclass_of()` calls.  There is a flag called only_subclass that 
allows there to be switching behavior in is_a_impl().

The issue has been updated with a new patch that now takes objects into 
account.  It also has a comment in there that better explains what the 
patch is doing.

I cannot assign it to you as I am not the original reporter, nor have 
access, can you assign it to yourself?

Thanks,
Ralph


> Hi Ralph,
>
> I agree with expected behavior, but didn't understand the patch and
> which side effects it may have as well as the original implementation of
> is_a_impl(). It looks for me like one huge bug :)
>
> Please reassign the bug to me, if you like me to take a deeper look.
> I can do it only on next week.
>
> Thanks. Dmitry.
>
> 
> > […]

---

## #53715 — Dmitry Stogov — 2011-07-01T06:55:29+00:00

URL: https://externals.io/message/53674#53715 · In reply to: #53711

Hi Ralph,

I reassigned it myself, and will take a look on Monday or Tuesday.

Thanks. Dmitry.



> Hey Dmitry,
>
> is_a_impl() is an implementation that is shared by `is_a()` and
> `is_subclass_of()` calls. There is a flag called only_subclass that allows
> there to be switching behavior in is_a_impl().
>
> The issue has been updated with a new patch that now takes objects into
> account. It also has a comment in there that better explains what the
> patch is doing.
>
> I cannot assign it to you as I am not the original reporter, nor have
> access, can you assign it to yourself?
>
> Thanks,
> Ralph
>
> 
> > […]

---

## #53741 — Dmitry Stogov — 2011-07-04T14:59:05+00:00

URL: https://externals.io/message/53674#53741 · In reply to: #53711

Hi Ralph,

Your patch was absolutely correct.
I've committed it with small improvements.

Thanks. Dmitry.


> Hey Dmitry,
>
> is_a_impl() is an implementation that is shared by `is_a()` and
> `is_subclass_of()` calls. There is a flag called only_subclass that allows
> there to be switching behavior in is_a_impl().
>
> The issue has been updated with a new patch that now takes objects into
> account. It also has a comment in there that better explains what the
> patch is doing.
>
> I cannot assign it to you as I am not the original reporter, nor have
> access, can you assign it to yourself?
>
> Thanks,
> Ralph
>
> 
> > […]