array_map/array_walk保持报告无效回调,未找到和/或未定义

function square($n) {
    return $n * $n;
}

$numbers = [1, 2, 3, 4, 5];
$squaredNumbers = array_map("square", $numbers);
print_r($squaredNumbers);

Array
(
    [0] => 1
    [1] => 4
    [2] => 9
    [3] => 16
    [4] => 25
)

function addPrefix(&$value, $key, $prefix) {
    $value = $prefix . $value;
}

$fruits = ["apple", "banana", "cherry"];
array_walk($fruits, "addPrefix", "fruit_");
print_r($fruits);

Array
(
    [0] => fruit_apple
    [1] => fruit_banana
    [2] => fruit_cherry
)