style: modify declaring empty slices (#2378)

* fix: modify declaring empty slices

declare an empty slice to var s []int replace s :=[]int{}, https://github.com/golang/go/wiki/CodeReviewComments#declaring-empty-slices

* fix lint

contrib/registry/eureka/register.go

@@ -92,12 +92,9 @@ func (r *Registry) Watch(ctx context.Context, serviceName string) (registry.Watc
 }
 
 func (r *Registry) Endpoints(service *registry.ServiceInstance) []Endpoint {
-	var (
-		res   = []Endpoint{}
-		start int
-	)
+	res := make([]Endpoint, 0, len(service.Endpoints))
 	for _, ep := range service.Endpoints {
-		start = strings.Index(ep, "//")
+		start := strings.Index(ep, "//")
 		end := strings.LastIndex(ep, ":")
 		appID := strings.ToUpper(service.Name)
 		ip := ep[start+2 : end]

middleware/tracing/span.go

@@ -57,10 +57,12 @@ func setClientSpan(ctx context.Context, span trace.Span, m interface{}) {
 }
 
 func setServerSpan(ctx context.Context, span trace.Span, m interface{}) {
-	attrs := []attribute.KeyValue{}
-	var remote string
-	var operation string
-	var rpcKind string
+	var (
+		attrs     []attribute.KeyValue
+		remote    string
+		operation string
+		rpcKind   string
+	)
 	tr, ok := transport.FromServerContext(ctx)
 	if ok {
 		operation = tr.Operation()