+ :param ptr: pointer to an initialized `memcached_st` struct
+ :param group_key: key namespace
+ :param group_key_length: length of the `group_key` without any trailing zero
+ :param key: the key to check
+ :param key_length: the length of the `key` without any trailing zero
+ :param value: the value to set
+ :param value_length: the length of the `value` without any trailing zero
+ :param expiration: expiration time as unix timestamp or relative time in seconds
+ :param flags: 16 bit flags
+ :param cas: the ``cas`` value to compare
+ :returns: `memcached_return_t` indicating success