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To: Arnold Daniels <arnold.adaniels.nl@gmail.com>,
 =?UTF-8?Q?Johannes_Schl=c3=bcter?= <johannes@schlueters.de>
Cc: PHP internals <internals@lists.php.net>, jan.h.boehmer@gmx.de
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Date: Sat, 28 Mar 2020 13:25:11 +0100
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Subject: Re: [PHP-DEV] [VOTE] Userspace operator overloading
From: cmbecker69@gmx.de ("Christoph M. Becker")

On 28.03.2020 at 10:22, Arnold Daniels wrote:

> This issues become even more apparent when sequencing operations like `$=
a +
> $b + $c - $d`. Trying left, then trying right, will make it very difficu=
lt
> to determine the outcome of such a statement.
>
> The arguments against type hinting for operator methods, assume the "try
> left/right" method. Instead, type hinting should be applied to determine
> which method should be used. If both or neither methods are applicable, =
an
> error must be thrown.

This "try left/right" approach is how operator overloading works for
internal classes[1], and apparently, it works quite well, as long as it
is not overused.

> With class inheritance, you also don't want to rely on the order of the
> operands. If you're the creator of a library, that's out of your hands. =
If
> both the parent and child class overwrite the operation, and both accept
> the operands, then the child class should always be used.

If a subclass overrides the operation, it would have to conform to
parameter type contravariance, so it would always be used, anyway.

[1]
<https://github.com/php/php-src/blob/php-7.4.4/Zend/zend_operators.h#L934-=
L937>

=2D-
Christoph M. Becker