php数组插入元素并保持键

$array = [1, 2, 3, 4];
$key = 2;
$value = 'new_value';

array_splice($array, $key, 0, $value);

print_r($array);

Array
(
    [0] => 1
    [1] => 2
    [2] => new_value
    [3] => 3
    [4] => 4
)

$array = [1, 2, 3, 4];
$key = 2;
$value = 'new_value';

$array = array_merge(array_slice($array, 0, $key), [$key => $value], array_slice($array, $key));

print_r($array);

Array
(
    [0] => 1
    [1] => 2
    [2] => new_value
    [3] => 3
    [4] => 4
)

$array = [1, 2, 3, 4];
$key = 2;
$value = 'new_value';

$keys = array_keys($array);
$keys = array_splice($keys, $key, 0, $key);
$array = array_combine($keys, $array);

print_r($array);

Array
(
    [0] => 1
    [1] => 2
    [2] => new_value
    [3] => 3
    [4] => 4
)