DOM: Add merge() method on ContainerBuilder

dom/container.go

@@ -190,6 +190,12 @@ func (c *containerBuilderImpl) Walk(fn WalkFn) {
 	}
 }
 
+func (c *containerBuilderImpl) Merge(other Container, opts ...MergeOption) ContainerBuilder {
+	m := &merger{}
+	m.init(opts...)
+	return m.mergeContainers(c, other)
+}
+
 func (c *containerBuilderImpl) AddList(name string) ListBuilder {
 	lb := &listBuilderImpl{}
 	c.add(name, lb)

dom/container_test.go

@@ -317,3 +317,15 @@ func TestContainerClone(t *testing.T) {
 	assert.Equal(t, 123, c2.Lookup("a.x.y").(Leaf).Value())
 	assert.Equal(t, "123", c2.Lookup("a.b[1]").(Leaf).Value())
 }
+
+func TestMergeContainers(t *testing.T) {
+	a := b.Container()
+	c := b.Container()
+	a.AddValueAt("l1.l2c", LeafNode(7))
+	a.AddValueAt("l1.l2d", LeafNode("0987"))
+	c.AddValueAt("l1.l2a", LeafNode("123"))
+	c.AddValueAt("l1.l2b", LeafNode("abc"))
+	d := c.Merge(a)
+	assert.Equal(t, 4, len(d.Lookup("l1").(Container).Children()))
+	assert.Equal(t, "abc", d.Lookup("l1.l2b").(Leaf).Value())
+}

dom/merge.go

@@ -77,7 +77,7 @@ func (mg *merger) mergeListsMeld(l1, l2 List) List {
 	return l
 }
 
-func (mg *merger) mergeContainers(c1, c2 Container) Container {
+func (mg *merger) mergeContainers(c1, c2 Container) ContainerBuilder {
 	merged := map[string]Node{}
 	for k, v := range c1.Children() {
 		merged[k] = v

dom/types.go

@@ -141,6 +141,8 @@ type ContainerBuilder interface {
 	RemoveAt(path string)
 	// Walk walks whole document tree, visiting every node
 	Walk(fn WalkFn)
+	// Merge creates new Container instance and merge current Container with other into it.
+	Merge(other Container, opts ...MergeOption) ContainerBuilder
 }
 
 type WalkFn func(path string, parent ContainerBuilder, node Node) bool