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To: Nikita Popov <nikita.ppv@gmail.com>, PHP internals
	<internals@lists.php.net>
Thread-Topic: [PHP-DEV] Re: [RFC] Arrow functions / short closures
Thread-Index: AQHU2nxyT92G5anxlkG9179pVR0E5aYLhuNt
Date: Thu, 14 Mar 2019 19:41:51 +0000
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Subject: Re: [PHP-DEV] Re: [RFC] Arrow functions / short closures
From: theodorejb@outlook.com (Theodore Brown)

On Thu, March 14, 2019 10:41 AM Nikita Popov <nikita.ppv@gmail.com> wrote:=
=0A=
=0A=
> On Wed, Mar 13, 2019 at 4:56 PM Nikita Popov <nikita.ppv@gmail.com> wrote=
:=0A=
> =0A=
> > Hi internals,=0A=
> >=0A=
> > Motivated by the recent list comprehensions RFC, I think it's time we t=
ook=0A=
> > another look at short closures:=0A=
> >=0A=
> > https://wiki.php.net/rfc/arrow_functions_v2=0A=
> =0A=
> As a small update, I've implemented a proof of concept that uses the ($x)=
=0A=
> =3D=3D> $x * $multiplier syntax (or $x =3D=3D> $x * $multiplier for short=
) in=0A=
> https://github.com/php/php-src/pull/3945. As mentioned in the RFC, this=
=0A=
> requires scanahead in the lexer.=0A=
> =0A=
> This syntax is in principle still on the table, though personally I prefe=
r=0A=
> fn($x, $y) =3D> $x * $y over ($x, $y) =3D=3D> $x * $y. The main redeeming=
 quality=0A=
> of =3D=3D> is that it supports the paren-less variant $x =3D=3D> $x. Taki=
ng into=0A=
> account the lexer hackery it requires (and which will also be required in=
=0A=
> any 3rd party tooling), this would not be my preferred choice.=0A=
>=0A=
=0A=
I agree that the nicest thing about this syntax is the ability to save=0A=
an additional 3 characters of boilerplate for the common use case of=0A=
single-parameter arrow functions. However, I'm also not a fan of adding=0A=
complex code hacks to make the syntax work.=0A=
=0A=
One alternative that doesn't seem to have had much discussion on list=0A=
is the `\($x) =3D> $x * $y` lambda syntax. This would also allow parenthese=
s=0A=
to be omitted for single parameters, making it just as terse as the =3D=3D>=
=0A=
syntax without the need for any lexer hackery.=0A=
=0A=
Here's how the examples from the RFC would look:=0A=
=0A=
```php=0A=
function array_values_from_keys($arr, $keys) {=0A=
    return array_map(\$x =3D> $arr[$x], $keys);=0A=
}=0A=
=0A=
=0A=
$extended =3D \$c =3D> $callable($factory($c), $c);=0A=
=0A=
=0A=
$this->existingSchemaPaths =3D array_filter($paths, \$v =3D> in_array($v, $=
names));=0A=
=0A=
=0A=
function complement(callable $f) {=0A=
    return \(...$args) =3D> !$f(...$args);=0A=
}=0A=
=0A=
=0A=
$result =3D Collection::from([1, 2])=0A=
    ->map(\$v =3D> $v * 2)=0A=
    ->reduce(\($tmp, $v) =3D> $tmp + $v, 0);=0A=
```=0A=
=0A=
One argument against this shorter syntax is that it wouldn't be as=0A=
easy to google as `fn`. However, long term I think everyone would=0A=
still get used to it, and I'm personally willing to add an answer=0A=
to the top Stack Overflow search result for "php backslash keyword".=0A=
=0A=
The backslash syntax has precedent from Haskell, and also wouldn't=0A=
introduce any BC break (who knows how many private codebases might=0A=
already have functions named `fn`).=0A=