btreeg: fix allocation in DeleteRange

btreeg.go

@@ -697,18 +697,26 @@ type DeleteRangeOptions struct {
 // Returns the deleted items as an ordered list that can be iterated over using
 // the list.Scan() method.
 func (tr *BTreeG[T]) DeleteRange(min, max T, opts *DeleteRangeOptions) (deleted List[T]) {
-	return tr.DeleteRangeReuse(min, max, opts, List[T]{})
+	return tr.DeleteRangeReuse(min, max, opts, &deleted)
 }
 
 // DeleteRangeReuse is the same as DeleteRange, but it takes a List as an argument to
 // avoid allocating/growing a new List on each call to DeleteRange. It is unsafe to use
 // the same List across concurrent calls to DeleteRange.
-func (tr *BTreeG[T]) DeleteRangeReuse(min, max T, opts *DeleteRangeOptions, deleted List[T]) List[T] {
+//
+// The deleted paramter needs to be a pointer as the go runtime can allocate a new backing memory on
+// append to a slice, and that change needs to be reflected in the caller.
+func (tr *BTreeG[T]) DeleteRangeReuse(min, max T, opts *DeleteRangeOptions, deleted *List[T]) List[T] {
 	if tr.lock(true) {
 		defer tr.unlock(true)
 	}
 	extract := opts == nil || !opts.NoReturn
 	maxincl := opts != nil && opts.MaxInclusive
+
+	if deleted == nil {
+		deleted = &List[T]{}
+	}
+
 	// Clear just in case it hasn't been cleared yet.
 	deleted.Clear()
 
@@ -730,7 +738,7 @@ func (tr *BTreeG[T]) DeleteRangeReuse(min, max T, opts *DeleteRangeOptions, dele
 	var stack []stackItem
 restart:
 	if tr.root == nil {
-		return deleted
+		return *deleted
 	}
 	n := tr.isoLoad(&tr.root, true)
 	stack = append(stack, stackItem{n, 0})
@@ -766,7 +774,7 @@ restart:
 			if found {
 				if maxstop(n.items[i]) {
 					// stop
-					return deleted
+					return *deleted
 				}
 				pivot = n.items[i]
 				if extract {
@@ -805,13 +813,13 @@ restart:
 			}
 			tr.count -= j
 			if stop {
-				return deleted
+				return *deleted
 			}
 		}
 		for ; i < len(n.items); i++ {
 			if maxstop(n.items[i]) {
 				// stop
-				return deleted
+				return *deleted
 			}
 			if len(n.items) > tr.min {
 				if extract {
@@ -841,7 +849,7 @@ restart:
 			stack = stack[:len(stack)-1]
 			if len(stack) == 0 {
 				// end of tree
-				return deleted
+				return *deleted
 			}
 			n = stack[len(stack)-1].node
 			if i < len(n.items) {