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Date: Sun, 27 Feb 2022 18:06:40 +0100
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To: Mel Dafert <mel@dafert.at>
Cc: internals <internals@lists.php.net>, Kamil Tekiela <tekiela246@gmail.com>
Content-Type: multipart/alternative; boundary="000000000000430a9f05d902f591"
Subject: Re: [PHP-DEV] Re: Proposal for RFC to remove undefined array index
 warning when used ina ternary
From: landers.robert@gmail.com (Robert Landers)

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On Sun, Feb 27, 2022 at 10:59 AM Mel Dafert <mel@dafert.at> wrote:

> On 27 February 2022 00:04:58 CET, Kamil Tekiela <tekiela246@gmail.com>
> wrote:
> >I just wanted to add that the following
> >
> >$name = $_POST['name'] ?: 'Default Name';
> >
> >with existence check would be
> >
> >$name = $_POST['name'] ?? null ?: 'Default Name';
> >
> >You don't need empty().
> >
> >I would be against changing the behaviour of elvis/ternary operator.
> >However, I remember seeing past suggestions to implement another operator.
> >One that would fill the gap between null-coalesce and elvis operators. If
> I
> >recall correctly, most of the time, these proposals end in consensus that
> >such operator isn't really needed. See
> >https://externals.io/message/89292#89292 and
> >https://externals.io/message/101606#101610
> >Maybe, it would be worthwhile to refresh a discussion about adding such
> >operator to the PHP language?
>
> I think that what would be needed here is another proposal from this
> discussion,
> something like a null-safe operator but for array access.
>
> From a different thread about this:
>
> On 15 February 2022 16:50:48 CET, Rowan Tommins <rowan.collins@gmail.com>
> wrote:
> >I seem to remember someone proposing an explicit operator for "this array
> dimension might not exist", something like this:
> >
> >if ( $array[?'key'] === true )
> >
> >Which would translate to:
> >
> >if ( (array_key_exists('key', $array) ? $array['key'] : null) === true )
>
> I would propose to extend this still to mean:
> `if((($array !== null && array_key_exists('key', $array)) ? $array['key']
> : null) === true)`
>
> This combines the above proposal with the behaviour of the nullsafe
> operator
> `?->`, allowing to signal that the array may be null or that the key may
> not be set.
>
> This allows the requested functionality without warnings/notices:
>
> $name = $_POST[?'name'] ?? 'Default Name';
>
> But also allows accessing arrays with multiple, possibly defined
> dimensions:
>
> $val = $array[?'a'][?'b'][?'c'] ?? 'default';
>
> Currently, the last example would need to be a rather unwieldy ternary:
>
> $val = (isset($array['a']) && isset($array['a']['b']) &&
> isset($array['a']['b']['c']) ? $array['a']['b']['c'] : 'default';
>

I've been writing it like this:

$val = (($array['a'] ?? [])['b'] ?? [])['c'] ?? 'default';

which is still unwieldy. I don't actually know if it is required to use []
vs. null, but it makes sense to use an empty array to me.


>
> The fact that the new syntax would also allow $array to be null may be
> undesirable in some cases, but I don't know if we can define the semantics
> in a better way.
> (Also, in some cases this may actually be useful, eg. when mixing ?-> and
> the new
> [?...] syntax.)


> I am not sure if the exact syntax/semantics proposed here are the best
> solution, but I would argue that the fact that this seems to be a
> recurring topic
> calls for a solution in that general direction.
>
>
I've been playing with a couple of syntaxes all day, but I think
$array[?$key] is growing on me. It isn't ambiguous or unwieldy. I did
discover an interesting case though:

['inner key' => $value] = $array[?'outer key'];

Right now ['key' => $value] = null; results in $value === null with no
warning. I'd personally prefer for it to be a warning, but might be out of
scope for this change, but if it were, maybe we'd want to use this syntax
if we did want null.

[?'inner key' => $value] = $array[?'outer key'];

I don't think list() operations will be a part of this RFC, FWIW.


> Regards,
> Mel
>

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