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To: Nikita Popov <nikita.ppv@gmail.com>
CC: "Christoph M. Becker" <cmbecker69@gmx.de>,Arnold Daniels <arnold.adaniels.nl@gmail.com>,PHP internals <internals@lists.php.net>,=?ISO-8859-1?Q?Jan_B=F6hmer?= <jan.h.boehmer@gmx.de>
Message-ID: <BD01F8AF-C8EA-4F41-9208-0F4169886AA2@schlueters.de>
Subject: Re: [PHP-DEV] [VOTE] Userspace operator overloading
From: johannes@schlueters.de (=?ISO-8859-1?Q?Johannes_Schl=FCter?=)



On March 28, 2020 5:44:28 PM GMT+01:00, Nikita Popov <nikita=2Eppv@gmail=
=2Ecom> wrote:
>On Sat, Mar 28, 2020 at 5:28 PM Johannes Schl=C3=BCter
><johannes@schlueters=2Ede>
>wrote:
>
>> On Sat, 2020-03-28 at 17:05 +0100, Christoph M=2E Becker wrote:
>> > On 28=2E03=2E2020 at 15:57, Johannes Schl=C3=BCter wrote:
>> >
>> > > On March 28, 2020 1:25:11 PM GMT+01:00, "Christoph M=2E Becker" <
>> > > cmbecker69@gmx=2Ede> wrote:
>> > >
>> > > > This "try left/right" approach is how operator overloading
>works
>> > > > for
>> > > > internal classes[1], and apparently, it works quite well, as
>long
>> > > > as it
>> > > > is not overused=2E
>> > >
>> > > The fact that it works in one or two cases as an implementation
>> > > detail where the full implementation is controlled by a single
>> > > group (internals) is no indication for it to work at large=2E
>> >
>> > Fair enough=2E  But maybe Python, where userland operator overloading
>> > works similar to the proposal at hand, is? :)
>>
>> It doesn't:
>>
>>
>> Python 3=2E6=2E9 (default, Nov  7 2019, 10:44:02)
>> [GCC 8=2E3=2E0] on linux
>> Type "help", "copyright", "credits" or "license" for more
>information=2E
>> >>> class A:
>> =2E=2E=2E     def __add__(self, other):
>> =2E=2E=2E         print("add")
>> =2E=2E=2E
>> >>> a =3D A()
>> >>> a + 1
>> add
>> >>> 1 + a
>> Traceback (most recent call last):
>>   File "<stdin>", line 1, in <module>
>> TypeError: unsupported operand type(s) for +: 'int' and 'A'
>>
>
>It does=2E
>
>Because Python uses instance methods for operator overloading, it has
>to
>use pairs of methods like __add__ and __radd__ to handle commuted
>variants=2E
>If you want to implement a commutative add, you need to implement both
>__add__ and __radd__=2E If __add__ is not implemented or returns
>NotImplemented, then __radd__ will be called=2E
>
>So, as Christoph has said, this is indeed the same system as what is
>being
>proposed here, with the difference that we do not need two separate
>methods
>per operator, but can use a static method instead=2E

If we use two methods as well it is a saner design=2E I won't like it, but=
 lot better than the current one=2E

johannes