def inject(span_context, format, carrier)
      case format
      when OpenTracing::FORMAT_TEXT_MAP, OpenTracing::FORMAT_BINARY, OpenTracing::FORMAT_RACK
        return nil
      else
        warn 'Unknown inject format'
      end
    end
def inject(span_context, format, carrier)
      case format
      when OpenTracing::FORMAT_TEXT_MAP, OpenTracing::FORMAT_BINARY, OpenTracing::FORMAT_RACK
        return nil
      else
        warn 'Unknown inject format'
      end
    end
Inject a SpanContext into the given carrier

 @param span_context [SpanContext]
 @param format [OpenTracing::FORMAT_TEXT_MAP, OpenTracing::FORMAT_BINARY, OpenTracing::FORMAT_RACK]
 @param carrier [Carrier] A carrier object of the type dictated by the specified `format`