BloombergLP::balm::MetricDescription::userData

Return the non‐modifiable value associated with the specified user‐data key. If the data for key has not been set, a value of 0 is returned, which is indistinguishable from a valid key with a 0 value. The behavior is undefined unless key >= 0. Note that this method allows clients of balm to access the (opaque) application‐specific information that they have previously associated with a metric (via setUserData).