use EmptySpanContext function instead of global variable (#86)

api/core/span_context.go

@@ -38,11 +38,10 @@ type SpanContext struct {
 	TraceOptions byte
 }
 
-var (
-	// INVALID_SPAN_CONTEXT is meant for internal use to return invalid span context during error
-	// conditions.
-	INVALID_SPAN_CONTEXT = SpanContext{}
-)
+// EmptySpanContext is meant for internal use to return invalid span context during error conditions.
+func EmptySpanContext() SpanContext {
+	return SpanContext{}
+}
 
 func (sc SpanContext) IsValid() bool {
 	return sc.HasTraceID() && sc.HasSpanID()

api/trace/noop_span.go

@@ -31,7 +31,7 @@ var _ Span = (*noopSpan)(nil)
 
 // SpancContext returns an invalid span context.
 func (noopSpan) SpanContext() core.SpanContext {
-	return core.INVALID_SPAN_CONTEXT
+	return core.EmptySpanContext()
 }
 
 // IsRecordingEvents always returns false for noopSpan.

sdk/trace/span.go

@@ -60,7 +60,7 @@ var _ apitrace.Span = &span{}
 
 func (s *span) SpanContext() core.SpanContext {
 	if s == nil {
-		return core.INVALID_SPAN_CONTEXT
+		return core.EmptySpanContext()
 	}
 	return s.spanContext
 }
@@ -225,7 +225,7 @@ func startSpanInternal(name string, parent core.SpanContext, remoteParent bool,
 
 	cfg := config.Load().(*Config)
 
-	if parent == core.INVALID_SPAN_CONTEXT {
+	if parent == core.EmptySpanContext() {
 		span.spanContext.TraceID = cfg.IDGenerator.NewTraceID()
 		noParent = true
 	}

sdk/trace/tracer.go

@@ -46,7 +46,7 @@ func (tr *tracer) Start(ctx context.Context, name string, o ...apitrace.SpanOpti
 	// 2. Remote is not trusted. In this case create a root span and then add the remote as link
 	//      span := tracer.Start(ctx, "some name")
 	//      span.Link(remote_span_context, ChildOfRelationship)
-	if opts.Reference.SpanContext != core.INVALID_SPAN_CONTEXT &&
+	if opts.Reference.SpanContext != core.EmptySpanContext() &&
 		opts.Reference.RelationshipType == apitrace.ChildOfRelationship {
 		parent = opts.Reference.SpanContext
 		remoteParent = true