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Date: Wed, 18 Sep 2013 16:48:49 +0200
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To: Sean Coates <sean@seancoates.com>
Cc: Leigh <leight@gmail.com>, PHP Development <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Re: Allowing is_* functions to accept multiple parameters
From: patrickallaert@php.net (Patrick ALLAERT)

2013/9/18 Sean Coates <sean@seancoates.com>:
>> i.e. is_null($a, $b, $c) would be the same as is_null($a) && is_null($b)
>> && is_null($c)
>
> Note that this would not be semantically equivalent in this form, even if `is_null()` did accept multiple parameters, because of the short-circuiting with `&&`:
>
> <?php
>
> function are_null() {
>         foreach (func_get_args() as $a) {
>                 if ($a !== null) {
>                         return false;
>                 }
>         }
>         return true;
> }
>
> function destroy_data() { echo "DESTROYING DATA\n"; }
>
> // old form: short-circuited; data is not destroyed
> if (is_null(null) && is_null(false) && is_null(destroy_data())) {
>         echo "All null.\n";
> } else {
>         echo "Not null.\n";
> }
>
> echo "----\n";
>
> // proposed form: no short-circuit; parameters are evaluated at call time and data is destroyed
> if (are_null(null, false, destroy_data())) {
>         echo "Still null.\n";
> } else {
>         echo "Still not null.\n";
> }
>

Not a good idea IMHO: it would complexify the execution a lot, think about:

$test = "are_null";

if ($test(null, false, destroy_data())) {
        echo "Still null.\n";
} else {
        echo "Still not null.\n";
}

Looking at the AST wouldn't be enough to tell what would or wouldn't
be short-circuited.

It looks fine to have is_* functions working on multiple values as
Leigh originally proposed. I also feel that it would mostly be
used/useful on variables.
People worrying about performance and/or execution of code with
short-circuiting can (and should) still rely on "&&".