type UntypedOpts … type UntypedFunc … // NewUntypedFunc creates a new UntypedFunc based on the provided // UntypedOpts. The value reported is determined by calling the given function // from within the Write method. Take into account that metric collection may // happen concurrently. If that results in concurrent calls to Write, like in // the case where an UntypedFunc is directly registered with Prometheus, the // provided function must be concurrency-safe. func NewUntypedFunc(opts UntypedOpts, function func() float64) UntypedFunc { … }