[RFC] On the need of a `is_int_string` ?

Hi,

When string is used as an array key, it's sometimes casted to an int.
As explained in https://www.php.net/manual/en/language.types.array.php:
"Strings containing valid decimal ints, unless the number is preceded by
a + sign, will be cast to the int type. E.g the key "8" will actually be
stored under 8. On the other 08 will not be cast as it isn't a valid
decimal integer."

This behavior cause some issues, especially for static analysis. As an
example https://phpstan.org/r/5a387113-de45-4bef-89af-b6c52adc5f69
vs real life https://3v4l.org/pDkoB

Currently most of static analysis rely on one/many native php functions to
describe types.
PHPStan/Psalm supports a numeric-string thanks to the is_numeric method.

I don't think there is a native function to know if the key will be casted
to an int. The implementation would be something similar (but certainly
better and in C) to

function is_int_string(string $s): bool
{
if (!is_numeric($s)) {
return false;
}

$a[$s] = $s;

return array_keys($a) !== array_values($a);
}

Which gives:
is_numeric('08') => true
ctype_digit('08') => true
is_int_string('08') => false

is_numeric('8') => true
ctype_digit('8') => true
is_int_string('8') => true

is_numeric('+8') => true
ctype_digit('+8') => false
is_int_string('+8') => false

is_numeric('8.4') => true
ctype_digit('8.4') => false
is_int_string('8.4') => false

Such method would allow to easily introduce a int-string type in static
analysis and the opposite, a non-int-string one (cf
https://github.com/phpstan/phpstan/issues/10239#issuecomment-1837571316).

WDYT about adding a is_int_string method then ?

Thanks

I found a simpler implementation later which rely on array_keys

fn is_int_string(string $s): bool => \is_int(array_keys([$s => null])[0]);

I considered that is_int_string was better in the same namespace than
is_object, is_array, is_int, is_numeric, ... but maybe there was something better
than int_string to describe this category of string since english is not good (integish ? integable ? integerable ?).
But indeed it could be interesting to relate this method to the array namespace...

Don't forget to bottom post!

I'm curious which one is faster/more efficient. :)

Anyway, this topic does not seems to interest lot of developer so far ^^'

I think it would be worth writing an RFC for. While super-niche feeling, I was literally bit by this the other day when storing what I thought were numbers as keys, but it turned out they got stored as strings (2-digit numbers, and the zero-prefix bit me). That being said, I'm not sure how this function would have helped me (other than tossing in a few asserts to make sure things were sane). So, writing an RFC will force you to think about usecases like that and some examples to highlight the issue it helps solve.

— Rob