fixup: standardise rhs of Merge dominates

report/latest_map_generated.go

@@ -30,8 +30,7 @@ func (m StringLatestMap) Size() int {
 }
 
 // Merge produces a StringLatestMap containing the keys from both inputs.
-// m must be at least as new as n
-// When both inputs contain the same key, the newer value is used.
+// When both inputs contain the same key, the value in 'n' is used.
 // Tries to return one of its inputs, if that already holds the correct result.
 func (m StringLatestMap) Merge(n StringLatestMap) StringLatestMap {
 	switch {
@@ -42,12 +41,12 @@ func (m StringLatestMap) Merge(n StringLatestMap) StringLatestMap {
 	}
 
 	i, j := 0, 0
-loop:
+loop: // go as far as we can get using elements from m
 	for i < len(m) {
 		switch {
 		case j >= len(n):
 			return m
-		case m[i].key == n[j].key:
+		case m[i] == n[j]:
 			i++
 			j++
 		case m[i].key < n[j].key:
@@ -69,7 +68,7 @@ loop:
 			out = append(out, m[i:]...)
 			return out
 		case m[i].key == n[j].key:
-			out = append(out, m[i])
+			out = append(out, n[j])
 			i++
 			j++
 		case m[i].key < n[j].key:

report/latest_map_internal_test.go

@@ -81,6 +81,14 @@ func TestLatestMapMerge(t *testing.T) {
 			want: MakeStringLatestMap().
 				Set("foo", "bar"),
 		},
+		"Identical a & b": {
+			a: MakeStringLatestMap().
+				Set("foo", "bar"),
+			b: MakeStringLatestMap().
+				Set("foo", "bar"),
+			want: MakeStringLatestMap().
+				Set("foo", "bar"),
+		},
 		"Disjoint a & b": {
 			a: MakeStringLatestMap().
 				Set("foo", "bar"),
@@ -90,20 +98,20 @@ func TestLatestMapMerge(t *testing.T) {
 				Set("foo", "bar").
 				Set("baz", "bop"),
 		},
-		"Common a & b": {
+		"Common a & b": { // b overrides a where there are keys in common
 			a: MakeStringLatestMap().
-				Set("foo", "bar"),
-			b: MakeStringLatestMap().
 				Set("foo", "baz"),
+			b: MakeStringLatestMap().
+				Set("foo", "bar"),
 			want: MakeStringLatestMap().
 				Set("foo", "bar"),
 		},
-		"Longer": {
+		"Longer": { // b overrides a where there are keys in common
 			a: MakeStringLatestMap().
-				Set("PID", "23128").
+				Set("PID", "0").
 				Set("Name", "curl"),
 			b: MakeStringLatestMap().
-				Set("PID", "0").
+				Set("PID", "23128").
 				Set("Name", "curl").
 				Set("Domain", "node-a.local"),
 			want: MakeStringLatestMap().
@@ -172,7 +180,7 @@ func TestLatestMapDecoding(t *testing.T) {
 {
   "bar": "baz",
   "foo": "bar",
-  "emptyval": 
+  "emptyval": ""
 }`
 	h := &codec.JsonHandle{}
 	decoder := codec.NewDecoder(bytes.NewBufferString(data), h)

report/node.go

@@ -158,7 +158,7 @@ func (n Node) WithChild(child Node) Node {
 
 // Merge mergses the individual components of a node and returns a
 // fresh node.
-// TODO: we must know at this point that n is at least as new as other
+// 'n' is taken to be older, and string values in 'other' will override
 func (n Node) Merge(other Node) Node {
 	id := n.ID
 	if id == "" {

report/report.go

@@ -352,7 +352,7 @@ func (r Report) Merge(other Report) Report {
 }
 
 // UnsafeMerge merges another Report into the receiver. The original is modified.
-// TODO: r must be at least as new as other
+// 'r' is taken to be older, and Node string values in 'other' will override
 func (r *Report) UnsafeMerge(other Report) {
 	r.DNS = r.DNS.Merge(other.DNS)
 	r.Sampling = r.Sampling.Merge(other.Sampling)

report/topology.go

@@ -191,6 +191,7 @@ func (t Topology) Merge(other Topology) Topology {
 }
 
 // UnsafeMerge merges the other object into this one, modifying the original.
+// 't' is taken to be older, and Node string values in 'other' will override
 func (t *Topology) UnsafeMerge(other Topology) {
 	if t.Shape == "" {
 		t.Shape = other.Shape
@@ -246,6 +247,7 @@ func (n Nodes) Copy() Nodes {
 }
 
 // Merge merges the other object into this one, and returns the result object.
+// 'n' is taken to be older, and Node string values in 'other' will override
 // The original is not modified.
 func (n Nodes) Merge(other Nodes) Nodes {
 	if len(other) > len(n) {
@@ -260,10 +262,11 @@ func (n Nodes) Merge(other Nodes) Nodes {
 }
 
 // UnsafeMerge merges the other object into this one, modifying the original.
+// 'n' is taken to be older, and Node string values in 'other' will override
 func (n *Nodes) UnsafeMerge(other Nodes) {
 	for k, v := range other {
 		if existing, ok := (*n)[k]; ok { // don't overwrite
-			(*n)[k] = v.Merge(existing)
+			(*n)[k] = existing.Merge(v)
 		} else {
 			(*n)[k] = v
 		}