library/Rediska/Key/Hash.php
public function offsetSet($field, $value)
    {
        if (is_null($field)) {
            throw new Rediska_Key_Exception('Field must be present');
        }

        $this->set($field, $value);

        return $value;
    }
public function offsetSet($field, $value)
    {
        if (is_null($field)) {
            throw new Rediska_Key_Exception('Field must be present');
        }

        $this->set($field, $value);

        return $value;
    }
Array magic for set a field

@param string $field
@param mixed $value
@return boolean