How Can I Distinguish Between Associative and Sequential Arrays in PHP?

Determining Associative vs Sequential Arrays in PHP

PHP maintains all arrays as associative, prompting the need for alternative methods to distinguish between associative and sequential arrays, particularly those containing only numerical keys starting from 0.

Solution: array_is_list() Function

PHP 8.1 introduces the array_is_list() function, providing a straightforward solution:

var_dump(array_is_list([])); // true
var_dump(array_is_list(['a', 'b', 'c'])); // true
var_dump(array_is_list([0 => 'a', 1 => 'b', 2 => 'c'])); // true
var_dump(array_is_list([1 => 'a', 0 => 'b', 2 => 'c'])); // false
var_dump(array_is_list(['a' => 'a', 'b' => 'b', 'c' => 'c'])); // false

Custom Function for Legacy Code:

If working with legacy code that does not support PHP 8.1, the following custom function can be employed:

function array_is_list(array $arr) {
    if ($arr === []) {
        return true;
    }
    return array_keys($arr) === range(0, count($arr) - 1);
}

This function achieves the same functionality as the array_is_list() function, making it portable across different PHP versions.

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