improve prependTreeNode

pkg/storage/tree/tree.go

@@ -81,31 +81,17 @@ func (t *Tree) Merge(srcTrieI merge.Merger) {
 
 		for _, srcChildNode := range st.ChildrenNodes {
 			dstChildNode := dt.insert(srcChildNode.Name)
-			srcNodes = prepend(srcNodes, srcChildNode)
-			dstNodes = prepend(dstNodes, dstChildNode)
+			srcNodes = prependTreeNode(srcNodes, srcChildNode)
+			dstNodes = prependTreeNode(dstNodes, dstChildNode)
 		}
 	}
 }
 
-func prepend(s []*treeNode, x *treeNode) []*treeNode {
-	if len(s) != 0 && s[0] == x {
-		return s
-	}
-	prev := x
-	for i, elem := range s {
-		switch {
-		case i == 0:
-			s[0] = x
-			prev = elem
-		case elem == x:
-			s[i] = prev
-			return s
-		default:
-			s[i] = prev
-			prev = elem
-		}
-	}
-	return append(s, prev)
+func prependTreeNode(s []*treeNode, x *treeNode) []*treeNode {
+	s = append(s, nil)
+	copy(s[1:], s)
+	s[0] = x
+	return s
 }
 
 func prependBytes(s [][]byte, x []byte) [][]byte {

pkg/storage/tree/tree_test.go

@@ -110,34 +110,17 @@ func treeStr(s string) string {
 }
 
 var _ = Describe("prepend", func() {
-	Context("prepend (treeNode)", func() {
-		A, B, C, X := &treeNode{}, &treeNode{}, &treeNode{}, &treeNode{}
-
-		It("prepend to slice with single elem", func() {
-			s := []*treeNode{A}
-			s = prepend(s, A)
-			Expect(s).To(HaveLen(1))
-			Expect(s[0]).To(Equal(A))
-		})
-
-		It("prepend slice with new elem", func() {
+	Context("prependTreeNode)", func() {
+		It("prepend elem", func() {
+			A, B, C, X := &treeNode{}, &treeNode{}, &treeNode{}, &treeNode{}
 			s := []*treeNode{A, B, C}
-			s = prepend(s, X)
+			s = prependTreeNode(s, X)
 			Expect(s).To(HaveLen(4))
 			Expect(s[0]).To(Equal(X))
 			Expect(s[1]).To(Equal(A))
 			Expect(s[2]).To(Equal(B))
 			Expect(s[3]).To(Equal(C))
 		})
-
-		It("prepend slice with existing elem", func() {
-			s := []*treeNode{A, B, C}
-			s = prepend(s, B)
-			Expect(s).To(HaveLen(3))
-			Expect(s[0]).To(Equal(B))
-			Expect(s[1]).To(Equal(A))
-			Expect(s[2]).To(Equal(C))
-		})
 	})
 	Context("prependBytes", func() {
 		It("prepend elem", func() {