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Message-ID: <C86ED976-5E52-428E-A824-0429601AB3FE@newclarity.net>
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Date: Sat, 19 Oct 2019 19:52:49 -0400
In-Reply-To: <CAP=w73VJ6pxstVzyfFkOp=esX7ne-LosWP1Eb8Ac0u-JeROPRA@mail.gmail.com>
Cc: PHP internals <internals@lists.php.net>
To: Kosit Supanyo <webdevxp.com@gmail.com>
References: <CAP=w73VJ6pxstVzyfFkOp=esX7ne-LosWP1Eb8Ac0u-JeROPRA@mail.gmail.com>
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 19, 2019, at 12:40 PM, Kosit Supanyo <webdevxp.com@gmail.com> =
wrote:
>=20
> Hi Internals
>=20
> I've just finished an implementation of 'switch-expression' that have =
been
> discussed recently. So I would like to present my ideas here.

This is great to see that you proactively implemented this.

> The basic syntax of switch-expression in this implementation is:
>=20
> $result =3D switch ($expr) {
>    case $cond1 =3D> $result1,
>    case $cond2 =3D> $result2,
>    case $cond3 =3D> $result3,
>    default =3D> $default_result,
> };

However, why the need to deviate with the existing syntax, making =
refactoring between switch statements and switch expressions more work =
that it needs to be.  Is there some reason why keeping colons and =
semlicolons would not work? =20

Given your syntax manually refactoring existing switches to use =
expressions, or refactoring back from expressions to statements will =
require more and tedious keystrokes than if you just kept colons and =
semicolons.  Is there a strong reason to change to using fat arrows and =
colons?


> You can omit parenthesized expression which is shortcut to `switch =
(true)`.
> This change applies to switch statement as well.
>=20
> $v =3D switch {
>    case $x >=3D 0 && $x <=3D 100 =3D> 1,
>    case $x >=3D 100 && $x <=3D 200 =3D> 2,
>    default =3D> 3,
> };
>=20
> switch {
>    case $x >=3D 0 && $x <=3D 100:
>        doSomething1();
>        break;
>    case $x >=3D 100 && $x <=3D 200:
>        doSomething2();
>        break;
>    default:
>        doNothing();
>        break;
> }

I do very much like this innovation.=20

Would love to see this work for switch statements too.

> You can also use `return` and `throw` in result expression. I recalled =
some
> languages have this feature (but I've forgotten what language). This
> feature can be very handy and useful in many use cases.
>=20
> $x =3D 'd';
> $v =3D switch ($x) {
>    case 'a' =3D> 1,
>    case 'b' =3D> 2,
>    case 'c' =3D> return true,
>    default =3D> throw new Exception("'$x' is not supported"),
> };

What about break? =20

> Additional feature in the demo patch is the 'type guard' unary =
operator
> which is an operator that will perform type check on given value and =
throw
> `TypeError` when type mismatch occurred, otherwise return the value as =
is.
> It has the same precedence  as `new`.
>=20
> $a =3D 'This is a string';
> $v =3D <int>$a; // TypeError: Value is expected to be int, string =
given
>=20
> Just like type hints, can accept nullable types.
>=20
> $v =3D <?int>switch ($x) {
>    case 'a' =3D> $result1,
>    case 'b' =3D> $result2,
> };

Nice!

-Mike


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