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Date: Mon, 23 Oct 2023 13:07:18 -0700
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To: Dik Takken <dik.takken@gmail.com>
Cc: internals@lists.php.net
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Subject: Re: [PHP-DEV] Custom object equality
From: jordan.ledoux@gmail.com (Jordan LeDoux)

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On Mon, Oct 23, 2023 at 10:20=E2=80=AFAM Dik Takken <dik.takken@gmail.com> =
wrote:

> On 23-10-2023 18:34, Larry Garfield wrote:
> >
> > Jordan's RFC explained in detail why interfaces are not viable, which i=
s
> why we have to use magic methods (with or without a special keyword)
> instead:
> >
> >
> https://wiki.php.net/rfc/user_defined_operator_overloads#why_not_interfac=
es
> >
> > (Seriously, it has an extensive FAQ.  It's one of the more detailed and
> supported RFCs we've seen.)
> >
>
> Yes, I know the RFC, it's a great piece of work! The use of interfaces
> as mentioned in this RFC is however completely different from what
> Pierre and I are talking about. If I understand Pierre correctly, that
> is. The suggestion to include interfaces simply meant to allow freedom
> of choice. Choice between using an operator (`=3D=3D`) or calling the
> equivalent method on the object (`->equals()`). That may get more people
> on board with operator overloading.
>
> Regards,
> Dik
>
>
I don't quite follow. The interface would cause the engine to use the
result of an `equals()` function on the object if it implements an
interface as part of `zend_compare`? Internally there is no `=3D=3D` functi=
on,
there is only the equivalent of `<=3D>`. To implement it ONLY for `=3D=3D` =
would
require a trapdoor of some kind in the `do_operation` handler that would
also affect the way the existing extensions work, such as the `DateTime`
class which implements a custom handler for the `compare` handler on the
zend class entry.

This might be easier to do once a few comparison improvements to separate
"comparable" and "equatable" are done, but the PR I submitted two years ago
to handle that got kind of mired in bike shedding about the implementation
and I lost interest in continuing to push it.

Implementing the compare handler for an overload requires adding two new
entries to ZEND_AST_BINARY_OP because the `>` and `<` comparisons have to
be preserved in the AST in order to call the correct object handler. THAT
requires updating OpCache and JIT since all such comparisons are currently
reordered to use `<`, and though I spent quite a while looking at it, I
think Dmitry might be the only person that could really implement that
fully. At least, I never found anyone that had the expertise to actually
help me with it.

Jordan

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