Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:121413
MIME-Version: 1.0
References: <CABAhh3FtvJ3TMF6R8Ot1o+OzS+SMOw37U3uehgCWPrP7guHB1A@mail.gmail.com>
In-Reply-To: <CABAhh3FtvJ3TMF6R8Ot1o+OzS+SMOw37U3uehgCWPrP7guHB1A@mail.gmail.com>
Date: Wed, 18 Oct 2023 19:20:23 +0200
Message-ID: <CANS-=pc3iYHrzPPLQU-M4RxhMXT50gemCBJ5ZGFRF1fE-6JW5Q@mail.gmail.com>
To: someniatko <someniatko@gmail.com>
Cc: php internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000462a68060800dcc3"
Subject: Re: [PHP-DEV] Custom object equality
From: kjarli@gmail.com (Lynn)

--000000000000462a68060800dcc3
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Wed, Oct 18, 2023 at 2:51=E2=80=AFPM someniatko <someniatko@gmail.com> w=
rote:

> Hi internals,
>
> There is often a need to compare whether two objects are equal. For
> example, a popular [brick/money](
> https://packagist.org/packages/brick/money)
> library has a `Money` class, which has an `equals()` method. However, thi=
s
> becomes tedious to implement such methods, when multiple nested objects a=
re
> involved. For instance, Money has an amount and a currency.
>
> There were already suggestions on the mailing list to allow "overloading"
> existing `=3D=3D` operator, and some suggestions went even as far as
> overloading `<`, `>=3D` etc operators. However, overloading existing
> operators may lead to a BC break between the PHP version which does suppo=
rt
> the functionality, and which doesn't. It won't result in a BC break in ca=
se
> it's an entirely new syntax, because a library or a project won't be able
> to write code which overloads `=3D=3D` in say PHP 8.4, but with code whic=
h
> still works in PHP 8.3 - it will have to require PHP 8.4+. But if it is
> implemented as a magic method, then `=3D=3D` will work differently for 8.=
3 and
> 8.4.
>
> I suggest thinking about introducing a new operator `~=3D`, which signifi=
es
> that custom equality is requested. In such a case,  `=3D=3D` will work as=
 it
> works now, and by default `~=3D` will work also like `=3D=3D`, unless its
> behavior is overwritten via a magic method. If a magic method is not
> present in a class being compared, `~=3D` will compare two objects field =
by
> field, but using `~=3D` comparison rather than `=3D=3D` comparison, recur=
sively.
>
> For instance, a Money object may consist of Amount and Currency. If two
> Moneys are compared using `~=3D`, and Money does not implement a magic
> method, Amount also doesn't implement it, but Currency does, then Amounts
> are compared using  `~=3D` which is equal to `=3D=3D` comparison in this =
case,
> but Currencies are compared using their custom comparison logic.
>
> This approach allows combining
> - no BC break - `~=3D` is a new syntax which is unavailable in older PHP
> versions
> - explicitly showing an intent that objects are compared using a custom
> comparison, rather than standard PHP one
> - allow to skip writing boilerplate equals() methods which just forward
> equals() to the nested objects
> - standardize such comparisons on the language level
>
> Of course how exactly this operator looks may be changed, `~=3D` is just =
an
> example.
>
> WDYT?
>
> Regards,
> Illia / someniatko
>

Note that `~=3D` is used in Lua instead of `!=3D`. Having this operator be =
an
overloading =3D=3D would feel really counterintuitive to me. We have
"instanceof", and I've seen "is" ideas floating around. Could also look
into the direction of "equals" for this.

https://www.lua.org/pil/3.2.html

--000000000000462a68060800dcc3--