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Date: Tue, 28 Apr 2020 17:10:31 +0200
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Subject: Re: [PHP-DEV] [VOTE] match expression
From: bobwei9@hotmail.com (Bob Weinand)



> Am 28.04.2020 um 12:48 schrieb Rowan Tommins <rowan.collins@gmail.com>:
>=20
> On Tue, 28 Apr 2020 at 11:19, Ilija Tovilo <tovilo.ilija@gmail.com> wrote=
:
>=20
>>> for the control-flow statement, it feels awkward and not in
>>> keeping with the rest of the language. If they were separate proposals,
>> the
>>> statement would probably end up looking very different.
>>=20
>> Can you elaborate? If I made a proposal exclusively for match
>> statements the syntax would be exactly equivalent.
>>=20
>=20
>=20
> If we take away the expression part, the proposal would be to replace thi=
s
> switch statement:
>=20
> switch ( $expr ) {
>     case 1:
>     case 2:
>           statement;
>     break;
>     default:
>           statement;
>     break;
> }
>=20
> With this match statement:
>=20
> match ( $expr ) {
>     1, 2 =3D> {
>           statement;
>     },
>     default =3D> {
>           statement;
>     },
> }
>=20
> The extra set of {} inside looks a little odd, but is a reasonable way to
> remove the implicit fallthrough. However, the other changes seem to just =
be
> arbitrarily new syntax:
>=20
> * No "case" keyword
> * =3D> instead of :
> * commas between statement blocks
>=20
> If the motivation is simply to fix the current switch statement, why not
> keep the syntax more familiar?
>=20
> match ( $expr ) {
>     case 1, 2: {
>           statement;
>     }
>     default: {
>           statement;
>     }
> }
>=20
> The colon looks unnecessary next to the opening brace, but if we keep it,
> the braces could be optional like they are in an if statement:
>=20
> match ( $expr ) {
>     case 1, 2: statement;
>     default: statement;
> }
>=20
> Note that this wouldn't suffer the problems of accidentally running code
> that you get with one-line if statements, because the following could
> simply be a syntax error:
>=20
> match ( $expr ) {
>     case 1, 2: statement; anotherStatement;
>     default: statement;
> }
>=20
>=20
> That syntax doesn't lend itself as well to being used as an expression, b=
ut
> I'm not convinced making one syntax work for both use cases is the right
> goal given the compromises it requires.
>=20
>=20
> Regards,
> --=20
> Rowan Tommins
> [IMSoP]

Hey Rowan,

I think you should first think about why the "case" needs to exists at all.=
 In particular it exists to distinguish goto labels from the case expressio=
ns in switch. With match, match restricting statements (and thus goto label=
s) into { brackets }, it now is not necessary to do such a distinction and =
we can get rid of the extra token.
"=3D>" is logical as well, we use the return value of the expressions (see =
fn() and array syntax), the colon is exclusively used for pure statement bo=
undaries.
The comma is necessary for the expression syntax at least (consider match($=
a) { 1 =3D> 2  + 2 + 2 =3D> 3 } - is this now match($a) { 1 =3D> 2, (2 + 2)=
 =3D> 3 } or match ($a) { 1 =3D> (2 + 2), +2 =3D> 3 } ?) You may argue to m=
ake it optional behind a statement block though.

Bob=