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Date: Mon, 21 Oct 2019 16:18:29 -0400
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To: Rowan Tommins <rowan.collins@gmail.com>
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Subject: Re: [PHP-DEV] 'switch-expression' and the 'type guard' unary operator
 demo
From: mike@newclarity.net (Mike Schinkel)

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> On Oct 21, 2019, at 11:12 AM, Rowan Tommins <rowan.collins@gmail.com> =
wrote:
>> What if in the future PHP implements variadic syntax for assigning to
>> arrays, e.g. $var =3D 1,2,3 where $var could satisfy a $variadic =
parameter
>> set of parameters w/o requiring `...`?   If PHP embraces that =E2=80=94=
 note GoLang
>> has something similar =E2=80=94 then will comma syntax allow for it =
with hacky use
>> of parentheses?
>> $y =3D  switch ($x) {
>>   case 1  =3D> $var =3D 1,2,3, $var[1],
>>   case -1  =3D> $var =3D 9,8,7, $var[1],
>>   default =3D> null,
>> };
>=20
> I'm not really clear what feature you're suggesting here, but I'm =
pretty
> sure it conflicts with existing uses of commas, so shouldn't constrain =
us
> from using them elsewhere.
>=20
> foo(1,2,3);
> foo($var =3D 1,2,3);
> $a =3D [0, $var =3D 1,2,3];
> // etc

You may well be right.=20

But to follow up to clarify what I was thinking consider the following =
(hypothetical) PHP syntax. Note that the return value has two comma =
separated values, and the assignment can accept those multiple values =
into two comma separated variables in the assignment:

function read_file(string $filepath):string,PHP\Error {
   $content =3D file_get_contents( $filepath );
   $error =3D false =3D=3D=3D $content
      ? new PHP\Error( "failed to open '%s'", $filepath )
      : null;
   return $content, $error;
}

$content, $err =3D read_file( __DIR__ . '/myfile.txt' );
if (!is_null( $err ) ) {
   error_log($err->message);
}
Now yes I know we can do this with arrays and list(), but I have never =
seen anyone do this in the wild and hence I think it is not idiomatic =
PHP. And I hypothesize they do not do this because it is ugly to read =
and write and because PHP will throw a runtime error (vs. load-time =
error) if you have fewer values returned than you assign:
function read_file( string $filepath ): array {
   $content =3D file_get_contents( $filepath );
   $error =3D false =3D=3D=3D $content
      ? new My\Error( "failed to open '%s'", $filepath )
      : null;

   return array( $content, $error );
}

list( $content, $err ) =3D read_file( __DIR__ . '/myfile.txt' );
if ( ! is_null( $err ) ) {
   error_log( $err->message );
}
With the first example PHP could type check at load time vs. having to =
wait for coverage of this code at runtime, and `:array` type hint in the =
latter is not as good as the `:string, PHP\Error` type hint of the =
former.

I am probably having unreasonable expectations to believe we will ever =
see this type of thing in PHP. Still I hold out hold and want to =
register an objection if I see new syntax that would make this syntax =
impossible in the future. #fwiw

-Mike


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