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Date: Tue, 15 Feb 2022 13:54:16 +0100
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Subject: Re: [PHP-DEV] Setting to disable the "Undefined array index" warning
From: a.leathley@gmx.net (Andreas Leathley)

On 15.02.22 13:31, Nicolas BADIA wrote:
> As it is explained in this ticket https://bugs.php.net/bug.php?id=3D8141=
7 we use to check if a property exists by accessing it directly like we do=
 in JavaScript.
>
> Personally, I subscribe to this coding style and we use it all over our =
codebase (more than 130 000 lines of PHP code). When it became a notice, w=
e disabled them, but now that it is a warning, it is a lot more problemati=
c for us=E2=80=A6 We can=E2=80=99t even use the last version of PHP Debug =
for VSCode.

The problem with your way of writing code is that it is ambiguous in
meaning, which is why this is a warning. You are not checking if a key
in an array exists, you are checking if an array value is "false-y". If
the value is an empty string, it is also interpreted as false, if it is
null, it is also interpreted as false, if it is an integer of value zero
it is also interpreted as false, if it is the string "0" it is also
interpreted as false.

When you write code as you do, it is easy to introduce subtle errors
because of these implicit casts. If you want to check if an array key is
defined, you should do it explicitly - this is not about a "coding
style", this is about writing the code in a way that actually does what
you intend it to do without it meaning multiple things of which some are
probably not expected. If you just want a quick fix without solving the
underlying problem, you can just add "?? null" to each array key access.

If you want to upgrade/improve your code base, which is a worthwhile
task, I would suggest the use of a static analyzer (like Psalm or
PHPStan) to find out where your code is ambigious. I have found many
undetected errors that way, where implicit casts have lead to unexpected
outcomes, which is why I am very much in favor of these warnings for
undefined array keys.