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Date: Mon, 30 Oct 2023 15:47:44 +0000
To: "php internals" <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Discussion - Anti-null coercion
From: larry@garfieldtech.com ("Larry Garfield")

On Mon, Oct 30, 2023, at 11:17 AM, Ilija Tovilo wrote:
> Hi Robert
>
> On Sun, Oct 29, 2023 at 7:31=E2=80=AFPM Robert Landers <landers.robert=
@gmail.com> wrote:
>>
>> Hello Internals,
>>
>> We currently have a null coercion operator: ??, but we lack an
>> anti-null coercion operator.
>> ...
>> fn() =3D>
>>   ($_SERVER['HTTP_X_MY_HEADER'] ?? null)
>>   ? md5($_SERVER['HTTP_X_MY_HEADER'])
>>   : null;
>> ...
>> This is rather tedious when you have to do it, so, I'd like to discuss
>> adding a new "anti-null coercion" operator: ?!
>>
>> This would collapse the previous verbose code into:
>>
>> fn() =3D>
>>   $_SERVER['HTTP_X_MY_HEADER']
>>   ?! md5($_SERVER['HTTP_X_MY_HEADER'];
>
> This does not seem significantly less verbose to me. The main
> motivation for ?? was that it avoids repeating the expression over
> something like ?:. I would see a stronger argument for this feature if
> it offered the same benefit. E.g.
>
> $_SERVER['HTTP_X_MY_HEADER'] ?! md5($$)
>
>> It would have a lower precedence than ?? so that the above line would
>> read from left to right without requiring parenthesis/brackets. The
>> operator would only return the right-hand side if the left-hand side
>> exists (aka, not null), otherwise, it would return null.
>
> I think it should have a higher precedence.
>
> $_SERVER['HTTP_X_MY_HEADER'] ?! md5($$) ?? 'abc'
> =3D=3D>
> ($_SERVER['HTTP_X_MY_HEADER'] ?! md5($$)) ?? 'abc'
>
> Otherwise the result is NULL if the header is missing, given that the
> coalesce operator is never executed.
>
> That said, while I've certainly encountered this situation, it's
> nothing a temporary variable can't fix. I don't personally believe
> there's a strong need for such an operator.
>
> Ilija

Another point to note is that for objects, we already have ?->, which ef=
fectively serves this purpose.  It is sugar for:

is_null($o) ? null : $o->whatever()

So any new operator would only be relevant for free-standing variables (=
which is automatically a code smell) or arrays, and I'm not convinced th=
e latter is a large enough use case in a decently written code base.  (Y=
ou really should know what your data is, and the best way to do that is =
map it into a proper object, at which point ?-> comes into play.)

--Larry Garfield