Hi @flobee! Omitting the => means you're omitting the key, not the value. As such, '-1' is assigned to the key 0. Moreover, numeric string keys get auto-coerced to integers. This is long standing behavior and cannot be changed without a significant BC break. See #9029 for more information. Changing this would at least require a discussion on the mailing list, and probably an RFC.

Though the question is then, why "-0" isn't auto-coerced to 0.

https://3v4l.org/SiJ6t

@heiglandreas @Girgias would probably be most informed about string to int coercion, but there is no -0 integer representation on most architectures. There is one for float, but floats are not valid array keys. As such $array['-0'] would be lossy, as it would be assigned to the same offset as $array['0'].

Thx. I remember, NOW :-) , from the very past. but was wondering.
The quotes give the right indication. For the 8 series
And since php8 so many many other things already works thousand of times better and correct since ever, i tought this was fixed also. While debugging an old parser, this came up! And still needs messi code to fix int values or assoc arrays may contain int which are obviosly strings.
Anyway! Thx for info.

Array keys do not follow the normal numeric string semantics. It has it own "integer string" semantics.

For example the offset '007' will not be changed to the integer offset 7 but '7' will.

Part of the technical background of the Saner Numeric Strings RFC explains this

@flobee No worries, thanks for your quick feedback!

Just to make it complet for other may need alterative help ways:
Using '+' sign in my example works because positiv ints never have a prefix.... and so a string as array key can be used that way.