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Date: Sun, 10 Apr 2011 16:04:06 +0200
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To: internals@lists.php.net
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Subject: Re: [PHP-DEV] Implicit isset/isempty check on short-ternary operator
From: rumi.kg@gmail.com (Rune Kaagaard)

Hey again

Updated here as always https://gist.github.com/909711. I've tried to
write down the goal of this new feature. Which patterns do we want to
make easier to write?

Do you agree with the goals I've set?

+1 From me of course :)

Also added a proposal that would make userland implementations possible.

## Goal ##
So what should be solved before this new feature can be considered a succes=
? The
solution should offer DRY solutions to the following patterns:

=A0 =A0// Set one variable from another or a default value.
=A0 =A0// 1a.
=A0 =A0$a =3D isset($b) ? $b : 'Default value';
=A0 =A0// 1b.
=A0 =A0$a =3D !empty($b) ? $b : 'Default value';

=A0 =A0// Set one variable from itself or a default value.
=A0 =A0// 2a.
=A0 =A0$a =3D isset($a) ? $a : 'Default value';
=A0 =A0// 2b.
=A0 =A0$a =3D !empty($a) ? $a : 'Default value';

=A0 =A0// Find the first set value from a range of variables and statements=
.
=A0 =A0// 3a.
=A0 =A0$tmp =3D get_value();
=A0 =A0if (isset($tmp)) $a =3D $tmp;
=A0 =A0$tmp =3D $myarr['mykey'];
=A0 =A0if (!isset($a) && isset($tmp)) $a =3D $tmp;
=A0 =A0if (!isset($a)) $a =3D 'Default value';

=A0 =A0// 3b.
=A0 =A0$tmp =3D get_value();
=A0 =A0if (!empty($tmp)) $a =3D $tmp;
=A0 =A0$tmp =3D $myarr['mykey'];
=A0 =A0if (!isset($a) && !empty($tmp)) $a =3D $tmp;
=A0 =A0if (!isset($a)) $a =3D 'Default value';

## Proposal 2 : Making a userland implementation possible ##
The one thing preventing us PHP end users for implementing our own solution=
 to
this problem is - as discussed many times before - that it is not possible =
to
check if a passed argument can be referenced and then reference it. This
proposal adds an `AS_REFERENCE` bitmask that can be passed as the second
argument to `func_get_arg` which then in turn throws an
`ArgNotReferencableException` if the argument is not referenceable.

Below is an example of how `firstset` (ifsetor) could be implemented.

=A0 =A0function firstset() {
=A0 =A0 =A0 =A0$num_args =3D func_num_args();
=A0 =A0 =A0 =A0for ($i =3D 0; $i < $num_args; ++$i) {
=A0 =A0 =A0 =A0 =A0 =A0try {
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0$arg =3D func_get_arg($i, AS_REFERENCE);
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (!isset($arg) {
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0$arg =3D null;
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0}
=A0 =A0 =A0 =A0 =A0 =A0} catch (ArgNotReferencableException $e) {
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0$arg =3D func_get_arg($i);
=A0 =A0 =A0 =A0 =A0 =A0}
=A0 =A0 =A0 =A0 =A0 =A0if (isset($arg) {
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0return $arg;
=A0 =A0 =A0 =A0 =A0 =A0}
=A0 =A0 =A0 =A0}
=A0 =A0 =A0 =A0return null;
=A0 =A0}