How can the usort function be effectively used to sort arrays in PHP?

The `usort` function in PHP can be effectively used to sort arrays based on a user-defined comparison function. This allows for custom sorting logic to be applied to the array elements. To use `usort`, you need to define a comparison function that returns -1, 0, or 1 based on the comparison of two elements. The `usort` function will then use this comparison function to sort the array accordingly.

// Define a comparison function for sorting by value length
function sortByLength($a, $b) {
    if (strlen($a) == strlen($b)) {
        return 0;
    }
    return (strlen($a) < strlen($b)) ? -1 : 1;
}

// Array to be sorted
$array = ["apple", "banana", "orange", "kiwi"];

// Sort the array using usort with the custom comparison function
usort($array, "sortByLength");

// Print the sorted array
print_r($array);