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Date: Sun, 25 Aug 2024 22:09:36 +0100
To: internals@lists.php.net
Subject: Re: [PHP-DEV] [RFC] Default expression
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")



On 25 August 2024 21:00:03 BST, Bilge <bilge@scriptfusion=2Ecom> wrote:
>class Suspension {
>=C2=A0=C2=A0=C2=A0 /**
>=C2=A0=C2=A0=C2=A0=C2=A0 * @param int $delay Specifies the delay in milli=
seconds=2E
>=C2=A0=C2=A0=C2=A0=C2=A0 */
>=C2=A0=C2=A0=C2=A0 public function suspend(int $delay =3D 1_000) {
>=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 var_dump($delay);
>=C2=A0=C2=A0=C2=A0 }
>}
>
>class MySuspension extends Suspension {
>=C2=A0=C2=A0=C2=A0 /**
>=C2=A0=C2=A0=C2=A0=C2=A0 * @param float|int|null $delay Specifies the del=
ay in seconds=2E
>=C2=A0=C2=A0=C2=A0=C2=A0 */
>=C2=A0=C2=A0=C2=A0 public function suspend(float|int|null $delay =3D null=
) {
>=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 parent::suspend((int)(($delay =
?? 0) * 1000) ?: default);
>=C2=A0=C2=A0=C2=A0 }
>}
>
>new MySuspension()->suspend(2=2E2345); // int(2234)
>
>Not only have I demonstrated the need to use multiplication or division t=
o change the scale, but also the need to cast=2E


Possibly something got lost as you redrafted the example, because as you'v=
e written it, neither the multiplication nor the cast are applied to the va=
lue looked up by "default"=2E The parameter reduces to "(expression) ?: def=
ault", which I've already agreed is useful=2E


I was thinking about why "bitwise or" feels so different from other operat=
ors here, and I realised it's because it's idempotent (I hope I'm using tha=
t term correctly): if the specified bits are already set, it will have no e=
ffect=2E

Consequently, we know that ($x | SOME_FLAG) & SOME_FLAG =3D=3D=3D SOME_FLA=
G without knowing the value of $x=2E That in turn means that regardless of =
how the default value changes in future, we know what "default | JSON_PRETT=
Y_PRINT" will do=2E

It's as though each bit flag is a separate parameter, and you're saying "p=
ass true to $prettyPrint, but let the implementation decide sensible defaul=
ts for all other flags"=2E

The majority of operators don't have that property, so they require some a=
dditional assumptions about the default, which might not hold in future=2E =
For instance, if you use "default + 1", you are implicitly assuming that th=
e default value is not the maximum allowed value=2E

Rowan Tommins
[IMSoP]