Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:109294
User-Agent: Cyrus-JMAP/3.1.7-1021-g152deaf-fmstable-20200319v1
Mime-Version: 1.0
Message-ID: <767910ef-d27b-404c-9ad1-037105c69d12@www.fastmail.com>
In-Reply-To: <4513B88E-CA5B-4DF2-94C8-242BEE54ADCC@me.com>
References: <047092C7-84FB-42AB-8084-7B83F76F55C1@me.com>
 <CABdc3WrX2M565H6af7axCgy=Kavairac8iVN4EkgtVCbu0H1mA@mail.gmail.com>
 <4513B88E-CA5B-4DF2-94C8-242BEE54ADCC@me.com>
Date: Wed, 25 Mar 2020 09:59:43 -0500
To: "php internals" <internals@lists.php.net>
Content-Type: text/plain;charset=utf-8
Content-Transfer-Encoding: quoted-printable
Subject: Re: [PHP-DEV] [RFC] switch expression
From: larry@garfieldtech.com ("Larry Garfield")

On Wed, Mar 25, 2020, at 9:27 AM, Ilija Tovilo wrote:
> Hi Micha=C5=82
>=20
> =20
>=20
> I=E2=80=99m sorry, unfortunately I missed your e-mail and RFC.
>=20
> Let me know if you=E2=80=99re still working on it and I=E2=80=99ll bac=
k off of course.
>=20
> =20
>=20
> Regards

I like the concept, and it looks like you're both on a similar track.  G=
ive or take details, I would very much like to see something like it.

One possible improvement to either version is allowing an expression on =
the left side.  That is, rather than doing an equality match, do a boole=
an match.  That would then allow:

$foo =3D switch($bar) {
  case $bar < 5 =3D> $bar * 3;
  case $baz < 10 =3D> $bar * 4;
  default =3D> $bar * 5;
};

That would sidestep the need for pattern matching, as you can do anythin=
g an expression can do.  The obvious caveat of course is figuring out ho=
w to reference the variable being switched on, if it's not already a var=
iable.  My first thought there is to borrow the $$ variable name from Sa=
ra's old function composition proposal, but there may be others.  There'=
s likely other issues to discuss here but allowing expressions on the le=
ft would greatly improve the expressiveness of the construct.

I'd prefer to not allow multi-line statements on the right, ie, blocks. =
 That leads to too much potential for long and ugly code, which a constr=
uct like this should be avoiding.  Limiting it to a single expression ke=
eps it compact; if you have more involved logic, then put it in a functi=
on and your expression is just... calling that function.  Problem solved=
.

Side note: I did a limited user-space implementation of the same concept=
 a while back:

https://hive.blog/php/@crell/type-matching-in-php

But I'd definitely rather see it in the native syntax.

--Larry Garfield