code: func MustInit(metrics interface{}, factory Factory, globalTags map[string]string) {
  	if err := Init(metrics, factory, globalTags); err != nil {
  		panic(err.Error())
  	}
  }
docs: // MustInit initializes the passed in metrics and initializes its fields using the passed in factory.
  //
  // It uses reflection to initialize a struct containing metrics fields
  // by assigning new Counter/Gauge/Timer values with the metric name retrieved
  // from the `metric` tag and stats tags retrieved from the `tags` tag.
  //
  // Note: all fields of the struct must be exported, have a `metric` tag, and be
  // of type Counter or Gauge or Timer.
  //
  // Errors during Init lead to a panic.