DefaultRecorder will be called for each Record call.
var DefaultRecorder func(tags *tag.Map, measurement interface{}, attachments map[string]interface{})
MeasurementRecorder will be called for each Record call. This is the same as DefaultRecorder but avoids interface{} conversion. This will be a func(tags *tag.Map, measurement []Measurement, attachments map[string]interface{}) type, but is interface{} here to avoid import loops
var MeasurementRecorder interface{}
SubscriptionReporter reports when a view subscribed with a measure.
var SubscriptionReporter func(measure string)