[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