ScardCommand
SCARD _key_
Time complexity O(1)Return the set cardinality (number of elements). If the key does notexist 0 is returned, like for empty sets. If the key does not holda set value -1 is returned. Client libraries should raise an errorwhen -1 is returned instead to pass the value to the caller.
Return value
Integer reply, specifically:the cardinality (number of elements) of the set as an integer `>=` 0 if the operation succeeded -2 if the specified key does not hold a set value