library/Rediska/Key/Set.php
public function add($value)
    {
        $result = $this->_getRediskaOn()->addToSet($this->getName(), $value);

        if (!is_null($this->getExpire()) && $result) {
            $this->expire($this->getExpire(), $this->isExpireTimestamp());
        }

        return $result;
    }
public function add($value)
    {
        $result = $this->_getRediskaOn()->addToSet($this->getName(), $value);

        if (!is_null($this->getExpire()) && $result) {
            $this->expire($this->getExpire(), $this->isExpireTimestamp());
        }

        return $result;
    }
Add the specified member to the Set

@param mixed $value Value
@return boolean