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To: Sergii Shymko <sergey@shymko.net>, Robert Landers
	<landers.robert@gmail.com>
CC: internals <internals@lists.php.net>
Thread-Topic: [PHP-DEV] Discussion - Anti-null coercion
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Date: Sun, 29 Oct 2023 20:02:03 +0000
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Subject: Re: [PHP-DEV] Discussion - Anti-null coercion
From: fabiocarpi@hotmail.com.br (Fabio Carpi)

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Following the php logic, maybe !??

________________________________
From: Sergii Shymko <sergey@shymko.net>
Sent: Sunday, October 29, 2023 4:53:12 PM
To: Robert Landers <landers.robert@gmail.com>
Cc: internals <internals@lists.php.net>
Subject: Re: [PHP-DEV] Discussion - Anti-null coercion



On Oct 29, 2023, at 1:31 PM, Robert Landers <landers.robert@gmail.com<mailt=
o:landers.robert@gmail.com>> wrote:

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

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Hi Robert,

Why don=92t you combine the two examples and use a regular ternary operator=
 along with isset/empty()?

fn() =3D>
  !empty($_SERVER[=91HTTP_X_MY_HEADER=92])
  ? md5($_SERVER[=91HTTP_X_MY_HEADER=92])
  : null;

It=92s only ever so slightly longer than the proposed ?! operator, but way =
more powerful. You explicitly control the evaluation expression along with =
the default value.

Regards,
Sergii

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