/**
 * @param $array 旧数组
 * @param $position 插入位置
 * @param $insert_array 新数组
 */
private function array_insert (&$array, $position, $insert_array) {
    $first_array = array_splice ($array, 0, $position);
    $array = array_merge ($first_array, $insert_array, $array);
}

    $data = [
        'a'=>1,
        'c'=>3,
        'd'=>4
    ];

    $newData = [
        'b'=>2,
    ];

    $this->array_insert($data,1,$newData);
    print_r($data);
    

// 结果 $data = ['a'=>1,'b'=>2,'c'=>3,'d'=>4]