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Date: Sun, 29 Oct 2023 21:23:54 +0100
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To: Sergii Shymko <sergey@shymko.net>
Cc: internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Discussion - Anti-null coercion
From: landers.robert@gmail.com (Robert Landers)

On Sun, Oct 29, 2023 at 8:53=E2=80=AFPM Sergii Shymko <sergey@shymko.net> w=
rote:
>
>
>
> On Oct 29, 2023, at 1:31 PM, Robert Landers <landers.robert@gmail.com> wr=
ote:
>
> Hello Internals,
>
> We currently have a null coercion operator: ??, but we lack an
> anti-null coercion operator.
>
> For example, if I wanted to operate on a header, if-and-only-if it
> exists, I'd have to write something like this one-liner:
>
> fn() =3D>
>  ($_SERVER['HTTP_X_MY_HEADER'] ?? null)
>  ? md5($_SERVER['HTTP_X_MY_HEADER'])
>  : null;
>
> Or something like this:
>
> function() {
>  if(!empty($_SERVER['HTTP_X_MY_HEADER']) {
>    return md5($_SERVER['HTTP_X_MY_HEADER']);
>  }
>
>  return 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'];
>
> When it is null, it will stay null, thus the above is the same as:
>
> fn() =3D>
>  $_SERVER['HTTP_X_MY_HEADER']
>  ?! md5($_SERVER['HTTP_X_MY_HEADER']
>  ?? null;
>
> 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'm not particularly attached to the ?! syntax (since it does, in
> fact, look very similar to ?:), so perhaps focusing on the merits of
> the idea first, then bikeshedding the syntax later would be a good
> approach?
>
> Thoughts?
>
> Robert Landers
> Software Engineer
> Utrecht NL
>
> --
> PHP Internals - PHP Runtime Development Mailing List
> To unsubscribe, visit: https://www.php.net/unsub.php
>
>
> Hi Robert,
>
> Why don=E2=80=99t you combine the two examples and use a regular ternary =
operator along with isset/empty()?
>
> fn() =3D>
>   !empty($_SERVER[=E2=80=98HTTP_X_MY_HEADER=E2=80=99])
>   ? md5($_SERVER[=E2=80=98HTTP_X_MY_HEADER=E2=80=99])
>   : null;
>
> It=E2=80=99s only ever so slightly longer than the proposed ?! operator, =
but way more powerful. You explicitly control the evaluation expression alo=
ng with the default value.
>
> Regards,
> Sergii

Hey Sergii,

> Why don=E2=80=99t you combine the two examples and use a regular ternary =
operator along with isset/empty()?

Because falsy is different than null/non-existent. The closest
equivalent is "array_key_exists" (instead of empty/isset) but this
proposal isn't just applicable to arrays. I run into this pattern of
"if not null, then do something with the value" pretty often and it is
tedious to type it out.

Robert Landers
Software Engineer
Utrecht NL