Add Iter Pos method.

btree.go

@@ -353,3 +353,11 @@ func (iter *Iter) Prev() bool {
 func (iter *Iter) Item() any {
 	return iter.base.Item()
 }
+
+// Pos returns the position of the current iterator item. Returns -1
+// if the tree is empty or the iterator is at the beginning of the tree.
+// Overall, the complexity will be O(log N⋅M) where stack height will
+// follow the height of the btree, which is log N, and M as the degree.
+func (iter *Iter) Pos() int {
+	return iter.base.Pos()
+}

btreeg.go

@@ -3,7 +3,9 @@
 // license that can be found in the LICENSE file.
 package btree
 
-import "sync"
+import (
+	"sync"
+)
 
 type BTreeG[T any] struct {
 	isoid        uint64
@@ -1323,6 +1325,34 @@ func (iter *IterG[T]) Item() T {
 	return iter.item
 }
 
+// Pos returns the position of the current iterator item. Returns -1
+// if the tree is empty or the iterator is at the beginning of the tree.
+// Overall, the complexity will be O(log N⋅M) where stack height will
+// follow the height of the btree, which is log N, and M as the degree.
+func (iter *IterG[T]) Pos() int {
+	if iter.tr == nil {
+		return -1
+	}
+	if !iter.seeked {
+		return -1
+	}
+	count := 0
+	for i, s := range iter.stack {
+		count += s.i
+		if !s.n.leaf() {
+			c := *s.n.children
+			t := s.i
+			if i == len(iter.stack)-1 {
+				t++
+			}
+			for j := 0; j < t; j++ {
+				count += c[j].count
+			}
+		}
+	}
+	return count
+}
+
 // Items returns all the items in order.
 func (tr *BTreeG[T]) Items() []T {
 	return tr.items(false)

btreeg_test.go

@@ -1343,3 +1343,26 @@ func TestGenericIterSeekPrefix(t *testing.T) {
 		iter.Release()
 	}
 }
+
+func TestGenericPos(t *testing.T) {
+	tr := NewBTreeG(func(a, b int) bool {
+		return a < b
+	})
+	count := 10_000
+	for i := 0; i < count; i++ {
+		tr.Set(i * 2)
+	}
+	iter := tr.Iter()
+	lastPos := iter.Pos()
+	assert(lastPos == -1)
+	iter.Release()
+	for i := 0; i < count; i++ {
+		iter = tr.Iter()
+		ret := iter.Seek(i*2 - 1)
+		assert(ret == true)
+		pos := iter.Pos()
+		assert(pos-lastPos == 1)
+		lastPos = pos
+		iter.Release()
+	}
+}