Merge pull request #7 from benbjohnson/sorted-map-builder

Add SortedMapBuilder

3 files changed, 280 insertions, 61 deletions

diff --git a/README.md b/README.md
index 653b9bb..c151641 100644
--- a/README.md
+++ b/README.md
@@ -263,7 +263,8 @@ built-in comparer implementations for `int`, `string`, and `[]byte` keys. You
 may pass a `nil` comparer to `NewSortedMap()` if you are using one of these key
 types.
 
-The API is identical to the `Map` implementation.
+The API is identical to the `Map` implementation. The sorted map also has a
+companion `SortedMapBuilder` for more efficiently building maps.
 
 
 ### Implementing a custom Comparer
diff --git a/immutable.go b/immutable.go
index 307b324..e8fac90 100644
--- a/immutable.go
+++ b/immutable.go
@@ -1577,6 +1577,10 @@ func (m *SortedMap) Get(key interface{}) (interface{}, bool) {
 
 // Set returns a copy of the map with the key set to the given value.
 func (m *SortedMap) Set(key, value interface{}) *SortedMap {
+	return m.set(key, value, false)
+}
+
+func (m *SortedMap) set(key, value interface{}, mutable bool) *SortedMap {
 	// Set a comparer on the first value if one does not already exist.
 	comparer := m.comparer
 	if comparer == nil {
@@ -1592,29 +1596,31 @@ func (m *SortedMap) Set(key, value interface{}) *SortedMap {
 		}
 	}
 
+	// Create copy, if necessary.
+	other := m
+	if !mutable {
+		other = m.clone()
+	}
+	other.comparer = comparer
+
 	// If no values are set then initialize with a leaf node.
 	if m.root == nil {
-		return &SortedMap{
-			size:     1,
-			root:     &sortedMapLeafNode{entries: []mapEntry{{key: key, value: value}}},
-			comparer: comparer,
-		}
+		other.size = 1
+		other.root = &sortedMapLeafNode{entries: []mapEntry{{key: key, value: value}}}
+		return other
 	}
 
 	// Otherwise delegate to root node.
 	// If a split occurs then grow the tree from the root.
 	var resized bool
-	newRoot, splitNode := m.root.set(key, value, comparer, &resized)
+	newRoot, splitNode := m.root.set(key, value, comparer, mutable, &resized)
 	if splitNode != nil {
 		newRoot = newSortedMapBranchNode(newRoot, splitNode)
 	}
 
-	// Return a new map with the new root.
-	other := &SortedMap{
-		size:     m.size,
-		root:     newRoot,
-		comparer: comparer,
-	}
+	// Update root and size (if resized).
+	other.size = m.size
+	other.root = newRoot
 	if resized {
 		other.size++
 	}
@@ -1624,23 +1630,38 @@ func (m *SortedMap) Set(key, value interface{}) *SortedMap {
 // Delete returns a copy of the map with the key removed.
 // Returns the original map if key does not exist.
 func (m *SortedMap) Delete(key interface{}) *SortedMap {
+	return m.delete(key, false)
+}
+
+func (m *SortedMap) delete(key interface{}, mutable bool) *SortedMap {
 	// Return original map if no keys exist.
 	if m.root == nil {
 		return m
 	}
 
 	// If the delete did not change the node then return the original map.
-	newRoot := m.root.delete(key, m.comparer)
-	if newRoot == m.root {
+	var resized bool
+	newRoot := m.root.delete(key, m.comparer, mutable, &resized)
+	if !resized {
 		return m
 	}
 
-	// Return new copy with the root and size updated.
-	return &SortedMap{
-		size:     m.size - 1,
-		root:     newRoot,
-		comparer: m.comparer,
+	// Create copy, if necessary.
+	other := m
+	if !mutable {
+		other = m.clone()
 	}
+
+	// Update root and size.
+	other.size = m.size - 1
+	other.root = newRoot
+	return other
+}
+
+// clone returns a shallow copy of m.
+func (m *SortedMap) clone() *SortedMap {
+	other := *m
+	return &other
 }
 
 // Iterator returns a new iterator for this map positioned at the first key.
@@ -1650,13 +1671,58 @@ func (m *SortedMap) Iterator() *SortedMapIterator {
 	return itr
 }
 
+// SortedMapBuilder represents an efficient builder for creating sorted maps.
+//
+// Maps returned from the builder are safe to use even after you continue to
+// use the builder. However, for efficiency, you should only retrieve your map
+// after you have completed building it.
+type SortedMapBuilder struct {
+	m       *SortedMap // current state
+	mutable bool       // if true, next mutation will operate in-place.
+}
+
+// NewSortedMapBuilder returns a new instance of SortedMapBuilder to build on a base map.
+func NewSortedMapBuilder(m *SortedMap) *SortedMapBuilder {
+	return &SortedMapBuilder{m: m}
+}
+
+// SortedMap returns the current copy of the map.
+// The returned map is safe to use even if after the builder continues to be used.
+func (b *SortedMapBuilder) Map() *SortedMap {
+	m := b.m
+	b.mutable = false
+	return m
+}
+
+// Len returns the number of elements in the underlying map.
+func (b *SortedMapBuilder) Len() int {
+	return b.m.Len()
+}
+
+// Get returns the value for the given key.
+func (b *SortedMapBuilder) Get(key interface{}) (value interface{}, ok bool) {
+	return b.m.Get(key)
+}
+
+// Set sets the value of the given key. See SortedMap.Set() for additional details.
+func (b *SortedMapBuilder) Set(key, value interface{}) {
+	b.m = b.m.set(key, value, b.mutable)
+	b.mutable = true
+}
+
+// Delete removes the given key. See SortedMap.Delete() for additional details.
+func (b *SortedMapBuilder) Delete(key interface{}) {
+	b.m = b.m.delete(key, b.mutable)
+	b.mutable = true
+}
+
 // sortedMapNode represents a branch or leaf node in the sorted map.
 type sortedMapNode interface {
 	minKey() interface{}
 	indexOf(key interface{}, c Comparer) int
 	get(key interface{}, c Comparer) (value interface{}, ok bool)
-	set(key, value interface{}, c Comparer, resized *bool) (sortedMapNode, sortedMapNode)
-	delete(key interface{}, c Comparer) sortedMapNode
+	set(key, value interface{}, c Comparer, mutable bool, resized *bool) (sortedMapNode, sortedMapNode)
+	delete(key interface{}, c Comparer, mutable bool, resized *bool) sortedMapNode
 }
 
 var _ sortedMapNode = (*sortedMapBranchNode)(nil)
@@ -1701,11 +1767,30 @@ func (n *sortedMapBranchNode) get(key interface{}, c Comparer) (value interface{
 }
 
 // set returns a copy of the node with the key set to the given value.
-func (n *sortedMapBranchNode) set(key, value interface{}, c Comparer, resized *bool) (sortedMapNode, sortedMapNode) {
+func (n *sortedMapBranchNode) set(key, value interface{}, c Comparer, mutable bool, resized *bool) (sortedMapNode, sortedMapNode) {
 	idx := n.indexOf(key, c)
 
 	// Delegate insert to child node.
-	newNode, splitNode := n.elems[idx].node.set(key, value, c, resized)
+	newNode, splitNode := n.elems[idx].node.set(key, value, c, mutable, resized)
+
+	// Update in-place, if mutable.
+	if mutable {
+		n.elems[idx] = sortedMapBranchElem{key: newNode.minKey(), node: newNode}
+		if splitNode != nil {
+			n.elems = append(n.elems, sortedMapBranchElem{})
+			copy(n.elems[idx+1:], n.elems[idx:])
+			n.elems[idx+1] = sortedMapBranchElem{key: splitNode.minKey(), node: splitNode}
+		}
+
+		// If the child splits and we have no more room then we split too.
+		if len(n.elems) > sortedMapNodeSize {
+			splitIdx := len(n.elems) / 2
+			newNode := &sortedMapBranchNode{elems: n.elems[:splitIdx:splitIdx]}
+			splitNode := &sortedMapBranchNode{elems: n.elems[splitIdx:]}
+			return newNode, splitNode
+		}
+		return n, nil
+	}
 
 	// If no split occurs, copy branch and update keys.
 	// If the child splits, insert new key/child into copy of branch.
@@ -1734,7 +1819,7 @@ func (n *sortedMapBranchNode) set(key, value interface{}, c Comparer, resized *b
 	// If the child splits and we have no more room then we split too.
 	if len(other.elems) > sortedMapNodeSize {
 		splitIdx := len(other.elems) / 2
-		newNode := &sortedMapBranchNode{elems: other.elems[:splitIdx]}
+		newNode := &sortedMapBranchNode{elems: other.elems[:splitIdx:splitIdx]}
 		splitNode := &sortedMapBranchNode{elems: other.elems[splitIdx:]}
 		return newNode, splitNode
 	}
@@ -1745,12 +1830,12 @@ func (n *sortedMapBranchNode) set(key, value interface{}, c Comparer, resized *b
 
 // delete returns a node with the key removed. Returns the same node if the key
 // does not exist. Returns nil if all child nodes are removed.
-func (n *sortedMapBranchNode) delete(key interface{}, c Comparer) sortedMapNode {
+func (n *sortedMapBranchNode) delete(key interface{}, c Comparer, mutable bool, resized *bool) sortedMapNode {
 	idx := n.indexOf(key, c)
 
 	// Return original node if child has not changed.
-	newNode := n.elems[idx].node.delete(key, c)
-	if newNode == n.elems[idx].node {
+	newNode := n.elems[idx].node.delete(key, c, mutable, resized)
+	if !*resized {
 		return n
 	}
 
@@ -1761,6 +1846,14 @@ func (n *sortedMapBranchNode) delete(key interface{}, c Comparer) sortedMapNode
 			return nil
 		}
 
+		// If mutable, update in-place.
+		if mutable {
+			copy(n.elems[idx:], n.elems[idx+1:])
+			n.elems[len(n.elems)-1] = sortedMapBranchElem{}
+			n.elems = n.elems[:len(n.elems)-1]
+			return n
+		}
+
 		// Return a copy without the given node.
 		other := &sortedMapBranchNode{elems: make([]sortedMapBranchElem, len(n.elems)-1)}
 		copy(other.elems[:idx], n.elems[:idx])
@@ -1768,6 +1861,12 @@ func (n *sortedMapBranchNode) delete(key interface{}, c Comparer) sortedMapNode
 		return other
 	}
 
+	// If mutable, update in-place.
+	if mutable {
+		n.elems[idx] = sortedMapBranchElem{key: newNode.minKey(), node: newNode}
+		return n
+	}
+
 	// Return a copy with the updated node.
 	other := &sortedMapBranchNode{elems: make([]sortedMapBranchElem, len(n.elems))}
 	copy(other.elems, n.elems)
@@ -1815,14 +1914,34 @@ func (n *sortedMapLeafNode) get(key interface{}, c Comparer) (value interface{},
 
 // set returns a copy of node with the key set to the given value. If the update
 // causes the node to grow beyond the maximum size then it is split in two.
-func (n *sortedMapLeafNode) set(key, value interface{}, c Comparer, resized *bool) (sortedMapNode, sortedMapNode) {
+func (n *sortedMapLeafNode) set(key, value interface{}, c Comparer, mutable bool, resized *bool) (sortedMapNode, sortedMapNode) {
 	// Find the insertion index for the key.
 	idx := n.indexOf(key, c)
+	exists := idx < len(n.entries) && c.Compare(n.entries[idx].key, key) == 0
+
+	// Update in-place, if mutable.
+	if mutable {
+		if !exists {
+			*resized = true
+			n.entries = append(n.entries, mapEntry{})
+			copy(n.entries[idx+1:], n.entries[idx:])
+		}
+		n.entries[idx] = mapEntry{key: key, value: value}
+
+		// If the key doesn't exist and we exceed our max allowed values then split.
+		if len(n.entries) > sortedMapNodeSize {
+			splitIdx := len(n.entries) / 2
+			newNode := &sortedMapLeafNode{entries: n.entries[:splitIdx:splitIdx]}
+			splitNode := &sortedMapLeafNode{entries: n.entries[splitIdx:]}
+			return newNode, splitNode
+		}
+		return n, nil
+	}
 
 	// If the key matches then simply return a copy with the entry overridden.
 	// If there is no match then insert new entry and mark as resized.
 	var newEntries []mapEntry
-	if idx < len(n.entries) && c.Compare(n.entries[idx].key, key) == 0 {
+	if exists {
 		newEntries = make([]mapEntry, len(n.entries))
 		copy(newEntries, n.entries)
 		newEntries[idx] = mapEntry{key: key, value: value}
@@ -1836,8 +1955,9 @@ func (n *sortedMapLeafNode) set(key, value interface{}, c Comparer, resized *boo
 
 	// If the key doesn't exist and we exceed our max allowed values then split.
 	if len(newEntries) > sortedMapNodeSize {
-		newNode := &sortedMapLeafNode{entries: newEntries[:len(newEntries)/2]}
-		splitNode := &sortedMapLeafNode{entries: newEntries[len(newEntries)/2:]}
+		splitIdx := len(newEntries) / 2
+		newNode := &sortedMapLeafNode{entries: newEntries[:splitIdx:splitIdx]}
+		splitNode := &sortedMapLeafNode{entries: newEntries[splitIdx:]}
 		return newNode, splitNode
 	}
 
@@ -1847,19 +1967,28 @@ func (n *sortedMapLeafNode) set(key, value interface{}, c Comparer, resized *boo
 
 // delete returns a copy of node with key removed. Returns the original node if
 // the key does not exist. Returns nil if the removed key is the last remaining key.
-func (n *sortedMapLeafNode) delete(key interface{}, c Comparer) sortedMapNode {
+func (n *sortedMapLeafNode) delete(key interface{}, c Comparer, mutable bool, resized *bool) sortedMapNode {
 	idx := n.indexOf(key, c)
 
 	// Return original node if key is not found.
 	if idx >= len(n.entries) || c.Compare(n.entries[idx].key, key) != 0 {
 		return n
 	}
+	*resized = true
 
 	// If this is the last entry then return nil.
 	if len(n.entries) == 1 {
 		return nil
 	}
 
+	// Update in-place, if mutable.
+	if mutable {
+		copy(n.entries[idx:], n.entries[idx+1:])
+		n.entries[len(n.entries)-1] = mapEntry{}
+		n.entries = n.entries[:len(n.entries)-1]
+		return n
+	}
+
 	// Return copy of node with entry removed.
 	other := &sortedMapLeafNode{entries: make([]mapEntry, len(n.entries)-1)}
 	copy(other.entries[:idx], n.entries[:idx])
diff --git a/immutable_test.go b/immutable_test.go
index ca2393b..9c3f548 100644
--- a/immutable_test.go
+++ b/immutable_test.go
@@ -1545,7 +1545,7 @@ func TestInternalSortedMapLeafNode(t *testing.T) {
 		for _, i := range rand.Perm(32) {
 			var resized bool
 			var splitNode sortedMapNode
-			node, splitNode = node.set(i, i*10, &cmpr, &resized)
+			node, splitNode = node.set(i, i*10, &cmpr, false, &resized)
 			if !resized {
 				t.Fatal("expected resize")
 			} else if splitNode != nil {
@@ -1578,11 +1578,11 @@ func TestInternalSortedMapLeafNode(t *testing.T) {
 		var node sortedMapNode = &sortedMapLeafNode{}
 		for _, i := range rand.Perm(32) {
 			var resized bool
-			node, _ = node.set(i, i*2, &cmpr, &resized)
+			node, _ = node.set(i, i*2, &cmpr, false, &resized)
 		}
 		for _, i := range rand.Perm(32) {
 			var resized bool
-			node, _ = node.set(i, i*3, &cmpr, &resized)
+			node, _ = node.set(i, i*3, &cmpr, false, &resized)
 			if resized {
 				t.Fatal("expected no resize")
 			}
@@ -1602,12 +1602,12 @@ func TestInternalSortedMapLeafNode(t *testing.T) {
 		var node sortedMapNode = &sortedMapLeafNode{}
 		for i := 0; i < 32; i++ {
 			var resized bool
-			node, _ = node.set(i, i*10, &cmpr, &resized)
+			node, _ = node.set(i, i*10, &cmpr, false, &resized)
 		}
 
 		// Add one more and expect split.
 		var resized bool
-		newNode, splitNode := node.set(32, 320, &cmpr, &resized)
+		newNode, splitNode := node.set(32, 320, &cmpr, false, &resized)
 
 		// Verify node contents.
 		newLeafNode, ok := newNode.(*sortedMapLeafNode)
@@ -1658,7 +1658,7 @@ func TestInternalSortedMapBranchNode(t *testing.T) {
 
 			var resized bool
 			var splitNode sortedMapNode
-			node, splitNode = node.set(key, key*10, &cmpr, &resized)
+			node, splitNode = node.set(key, key*10, &cmpr, false, &resized)
 			if key == leaf0.entries[0].key || key == leaf1.entries[0].key {
 				if resized {
 					t.Fatalf("expected no resize: key=%d", key)
@@ -1701,7 +1701,7 @@ func TestInternalSortedMapBranchNode(t *testing.T) {
 
 		// Add one more and expect split.
 		var resized bool
-		newNode, splitNode := node.set((32 * 32), (32*32)*100, &cmpr, &resized)
+		newNode, splitNode := node.set((32 * 32), (32*32)*100, &cmpr, false, &resized)
 
 		// Verify node contents.
 		var idx int
@@ -1843,7 +1843,7 @@ func TestSortedMap_Set(t *testing.T) {
 	})
 
 	RunRandom(t, "Random", func(t *testing.T, rand *rand.Rand) {
-		m := NewTestSortedMap()
+		m := NewTSortedMap()
 		for j := 0; j < 10000; j++ {
 			switch rand.Intn(2) {
 			case 1: // overwrite
@@ -1950,7 +1950,7 @@ func TestSortedMap_Delete(t *testing.T) {
 	})
 
 	RunRandom(t, "Random", func(t *testing.T, rand *rand.Rand) {
-		m := NewTestSortedMap()
+		m := NewTSortedMap()
 		for j := 0; j < 10000; j++ {
 			switch rand.Intn(8) {
 			case 0: // overwrite
@@ -1966,6 +1966,16 @@ func TestSortedMap_Delete(t *testing.T) {
 		if err := m.Validate(); err != nil {
 			t.Fatal(err)
 		}
+
+		// Delete all keys.
+		keys := make([]int, len(m.keys))
+		copy(keys, m.keys)
+		for _, k := range keys {
+			m.Delete(k)
+		}
+		if err := m.Validate(); err != nil {
+			t.Fatal(err)
+		}
 	})
 }
 
@@ -2057,21 +2067,23 @@ func TestSortedMap_Iterator(t *testing.T) {
 	})
 }
 
-// TestSortedMap represents a combined immutable and stdlib sorted map.
-type TestSortedMap struct {
+// TSortedMap represents a combined immutable and stdlib sorted map.
+type TSortedMap struct {
 	im, prev *SortedMap
+	builder  *SortedMapBuilder
 	std      map[int]int
 	keys     []int
 }
 
-func NewTestSortedMap() *TestSortedMap {
-	return &TestSortedMap{
-		im:  NewSortedMap(nil),
-		std: make(map[int]int),
+func NewTSortedMap() *TSortedMap {
+	return &TSortedMap{
+		im:      NewSortedMap(nil),
+		builder: NewSortedMapBuilder(NewSortedMap(nil)),
+		std:     make(map[int]int),
 	}
 }
 
-func (m *TestSortedMap) NewKey(rand *rand.Rand) int {
+func (m *TSortedMap) NewKey(rand *rand.Rand) int {
 	for {
 		k := rand.Int()
 		if _, ok := m.std[k]; !ok {
@@ -2080,16 +2092,17 @@ func (m *TestSortedMap) NewKey(rand *rand.Rand) int {
 	}
 }
 
-func (m *TestSortedMap) ExistingKey(rand *rand.Rand) int {
+func (m *TSortedMap) ExistingKey(rand *rand.Rand) int {
 	if len(m.keys) == 0 {
 		return 0
 	}
 	return m.keys[rand.Intn(len(m.keys))]
 }
 
-func (m *TestSortedMap) Set(k, v int) {
+func (m *TSortedMap) Set(k, v int) {
 	m.prev = m.im
 	m.im = m.im.Set(k, v)
+	m.builder.Set(k, v)
 
 	if _, ok := m.std[k]; !ok {
 		m.keys = append(m.keys, k)
@@ -2098,9 +2111,10 @@ func (m *TestSortedMap) Set(k, v int) {
 	m.std[k] = v
 }
 
-func (m *TestSortedMap) Delete(k int) {
+func (m *TSortedMap) Delete(k int) {
 	m.prev = m.im
 	m.im = m.im.Delete(k)
+	m.builder.Delete(k)
 	delete(m.std, k)
 
 	for i := range m.keys {
@@ -2111,26 +2125,41 @@ func (m *TestSortedMap) Delete(k int) {
 	}
 }
 
-func (m *TestSortedMap) Validate() error {
+func (m *TSortedMap) Validate() error {
 	for _, k := range m.keys {
 		if v, ok := m.im.Get(k); !ok {
 			return fmt.Errorf("key not found: %d", k)
 		} else if v != m.std[k] {
 			return fmt.Errorf("key (%d) mismatch: immutable=%d, std=%d", k, v, m.std[k])
 		}
+		if v, ok := m.builder.Get(k); !ok {
+			return fmt.Errorf("builder key not found: %d", k)
+		} else if v != m.std[k] {
+			return fmt.Errorf("builder key (%d) mismatch: immutable=%d, std=%d", k, v, m.std[k])
+		}
+	}
+
+	if got, exp := m.builder.Len(), len(m.std); got != exp {
+		return fmt.Errorf("SortedMapBuilder.Len()=%d, expected %d", got, exp)
 	}
 
 	sort.Ints(m.keys)
-	if err := m.validateForwardIterator(); err != nil {
-		return err
-	} else if err := m.validateBackwardIterator(); err != nil {
-		return err
+	if err := m.validateForwardIterator(m.im); err != nil {
+		return fmt.Errorf("basic: %s", err)
+	} else if err := m.validateBackwardIterator(m.im); err != nil {
+		return fmt.Errorf("basic: %s", err)
+	}
+
+	if err := m.validateForwardIterator(m.builder.Map()); err != nil {
+		return fmt.Errorf("basic: %s", err)
+	} else if err := m.validateBackwardIterator(m.builder.Map()); err != nil {
+		return fmt.Errorf("basic: %s", err)
 	}
 	return nil
 }
 
-func (m *TestSortedMap) validateForwardIterator() error {
-	itr := m.im.Iterator()
+func (m *TSortedMap) validateForwardIterator(mm *SortedMap) error {
+	itr := mm.Iterator()
 	for i, k0 := range m.keys {
 		v0 := m.std[k0]
 		if k1, v1 := itr.Next(); k0 != k1 || v0 != v1 {
@@ -2148,8 +2177,8 @@ func (m *TestSortedMap) validateForwardIterator() error {
 	return nil
 }
 
-func (m *TestSortedMap) validateBackwardIterator() error {
-	itr := m.im.Iterator()
+func (m *TSortedMap) validateBackwardIterator(mm *SortedMap) error {
+	itr := mm.Iterator()
 	itr.Last()
 	for i := len(m.keys) - 1; i >= 0; i-- {
 		k0 := m.keys[i]
@@ -2222,6 +2251,29 @@ func BenchmarkSortedMap_Iterator(b *testing.B) {
 	})
 }
 
+func BenchmarkSortedMapBuilder_Set(b *testing.B) {
+	b.ReportAllocs()
+	builder := NewSortedMapBuilder(NewSortedMap(nil))
+	for i := 0; i < b.N; i++ {
+		builder.Set(i, i)
+	}
+}
+
+func BenchmarkSortedMapBuilder_Delete(b *testing.B) {
+	const n = 1000000
+
+	builder := NewSortedMapBuilder(NewSortedMap(nil))
+	for i := 0; i < n; i++ {
+		builder.Set(i, i)
+	}
+	b.ReportAllocs()
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		builder.Delete(i % n)
+	}
+}
+
 func ExampleSortedMap_Set() {
 	m := NewSortedMap(nil)
 	m = m.Set("foo", "bar")
@@ -2286,6 +2338,43 @@ func ExampleSortedMap_Iterator() {
 	// strawberry 900
 }
 
+func ExampleSortedMapBuilder_Set() {
+	b := NewSortedMapBuilder(NewSortedMap(nil))
+	b.Set("foo", "bar")
+	b.Set("baz", 100)
+
+	m := b.Map()
+	v, ok := m.Get("foo")
+	fmt.Println("foo", v, ok)
+
+	v, ok = m.Get("baz")
+	fmt.Println("baz", v, ok)
+
+	v, ok = m.Get("bat") // does not exist
+	fmt.Println("bat", v, ok)
+	// Output:
+	// foo bar true
+	// baz 100 true
+	// bat <nil> false
+}
+
+func ExampleSortedMapBuilder_Delete() {
+	b := NewSortedMapBuilder(NewSortedMap(nil))
+	b.Set("foo", "bar")
+	b.Set("baz", 100)
+	b.Delete("baz")
+
+	m := b.Map()
+	v, ok := m.Get("foo")
+	fmt.Println("foo", v, ok)
+
+	v, ok = m.Get("baz")
+	fmt.Println("baz", v, ok)
+	// Output:
+	// foo bar true
+	// baz <nil> false
+}
+
 // RunRandom executes fn multiple times with a different rand.
 func RunRandom(t *testing.T, name string, fn func(t *testing.T, rand *rand.Rand)) {
 	if testing.Short() {