question: returns the set of tag names concode_field_sep MetricMap metricMap concode_elem_sep TagMap tagMap concode_field_sep TagMap getTagsCopy concode_elem_sep MetricMap getMetricsCopy concode_elem_sep Number getMetric concode_elem_sep Object getTag concode_elem_sep Set<String> getMetricNames
target: Set < String > function ( ) { return Collections . unmodifiableSet ( tagMap . keySet ( ) ) ; }