type SpanContext … type Span … type contextKeyType … const spanContextKey … const labelContextKey … func GetSpan(ctx context.Context) *Span { … } // Spans creates an exporter that maintains hierarchical span structure in the // context. // It creates new spans on start events, adds events to the current span on // log or label, and closes the span on end events. // The span structure can then be used by other exporters. func Spans(output event.Exporter) event.Exporter { … } func (s *SpanContext) Format(f fmt.State, r rune) { … } func (s *Span) Start() core.Event { … } func (s *Span) Finish() core.Event { … } func (s *Span) Events() []core.Event { … } func (s *Span) Format(f fmt.State, r rune) { … }