Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:108817
MIME-Version: 1.0
References: <005101d5edae$7b7c3e10$7274ba30$@gmx.de> <479ea7da1e5738d7bed6c8dd773c@news.php.net>
In-Reply-To: <479ea7da1e5738d7bed6c8dd773c@news.php.net>
Date: Tue, 3 Mar 2020 09:52:52 +0000
Message-ID: <CALKiJKpe_uejb9v=kCHQ_kKWJAXHJPwFaXTbf5Du_Nwp5kTkOA@mail.gmail.com>
Cc: PHP internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000192d85059ff0458d"
Subject: Re: [PHP-DEV] Re: [RFC] Userspace operator overloading
From: rowan.collins@gmail.com (Rowan Tommins)

--000000000000192d85059ff0458d
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

Hi Terje,

I think both of your examples are compatible with the idea of grouped
operators, as long as we don't constrain a type to implement all operators
with the same right-hand side.


On Mon, 2 Mar 2020 at 17:23, Terje Sletteb=C3=B8 <
terje.slettebo@sandefjordbredband.net> wrote:

>
> Adding and subtracting money makes sense, but it makes no sense to
> multiply
> or divide them, and this is just *one* domain.
>


This is true, but it does make sense to multiply and divide them by
numbers, for instance $totalPrice =3D $unitPrice * $quantity

In general, if $a + $a represents addition, then $a * 2 should logically
give the same result. As has been raised, there is an argument for keeping
/ separate, for types that cannot handle fractional operations; it would be
a matter of choice whether $price / 2 should be supported because it would
lead to fractional pennies/cents.



> $total_discount =3D $total * $discount;
>
> Here, $total_discount and $total is Money, while $discount is a
> Percentage,
> so we should be able to define a method that allows you to multiply Money
> with Percentage, and return a Money object. Adding Money and Percentage
> would
> make no sense, but multiplying them does.
>


If this operator was implemented in isolation, it would again be drifting
into domain-specific language territory. (I don't personally have a problem
with that, but many people vocally object to it.)

However, it could easily be made part of a consistent set of arithmetic
operators:

On class Money:

Money + Money =3D> Money
Money - Money =3D> Money
Money * int =3D> Money
Money / int =3D> Money
int * Money =3D> Money
int / Money =3D> Error
Money * Percentage =3D> Money
Money / Percentage =3D> Money
Percentage * Money =3D> Money
Percentage / Money =3D> Error

Optionally, on class Percentage:

Percentage + Percentage =3D> Percentage
Percentage - Percentage =3D> Percentage
Percentage* int =3D> Percentage
Percentage / int =3D> Percentage



Regards,
--=20
Rowan Tommins
[IMSoP]

--000000000000192d85059ff0458d--