数组

class Arr
{
    public $data = [];
    public $len = 0;

    public function push($value, $index = -1)
    {

        if ($index != -1 && $index > $this->len) {
            throw new \Exception('index out of range');
        }

        if ($index == -1 || $index == $this->len) {
            $this->data[$this->len] = $value;
            $this->len++;
            return true;
        } else {
            for ($i = $this->len - 1; $i >= $index; $i--) {
                $this->data[$i + 1] = $this->data[$i];
            }
            $this->data[$index] = $value;
            $this->len++;
            return true;
        }
    }

    public function pop($index = -1)
    {

        if ($this->len <= 0) {
            throw new \Exception('array is empty');
        }

        if ($index != -1 && $index >= $this->len) {
            throw new \Exception('index out of range');
        }

        if ($index == -1 || $index == $this->len - 1) {
            $this->len--;
            $value = $this->data[$this->len];
            unset($this->data[$this->len]);
            return $value;
        } else {
            $this->len--;
            $value = $this->data[$index];
            for ($i = $index; $i < $this->len; $i++) {
                $this->data[$i] = $this->data[$i + 1];
            }
            unset($this->data[$this->len]);
            return $value;
        }
    }

    public function set($index, $value)
    {
        if ($index < 0 || $index >= $this->len) {
            throw new \Exception('index out of range');
        }

        $this->data[$index] = $value;
    }

    public function get($index)
    {
        if ($index < 0 || $index >= $this->len) {
            throw new \Exception('index out of range');
        }
        return $this->data[$index];
    }

    public function lists()
    {
        return $this->data;
    }
}