var once sync.Once

// Init initializes OpenTelemetry SDK and uses OTel-OpenTracing Bridge
// to return an OpenTracing-compatible tracer.
func Init(serviceName string, exporterType string, ...) opentracing.Tracer {
	once.Do(func() {
		propagation.NewCompositeTextMapPropagator(
			propagation.TraceContext{},
			propagation.Baggage{},
		))
	})
  // ...
}