Flatten Multi-Dimensional Array Recursively

function flattenArray(array $array): array {
    $result = [];
    array_walk_recursive($array, function($item) use (&$result) {
        $result[] = $item;
    });
    return $result;
}

$multiDimensionalArray = [
    'a' => 1,
    'b' => ['c' => 2, 'd' => 3],
    'e' => [4, ['f' => 5, 'g' => 6]],
    7
];

$flatArray = flattenArray($multiDimensionalArray);
print_r($flatArray);
// Output: Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 [5] => 6 [6] => 7 )

How it works: This snippet provides a function `flattenArray` that takes any multi-dimensional PHP array and converts it into a single-dimensional array. It leverages `array_walk_recursive`, a built-in PHP function that applies a user-defined callback function to every scalar value in an array. The callback captures the `$result` array by reference, appending each scalar item it encounters during the recursive traversal, effectively 'flattening' the structure.