RangeModification: add is_no_op/is_reinitialization

libs/persistent_range_query/src/lib.rs

@@ -36,6 +36,8 @@ pub trait RangeModification<Key> {
     type Result: RangeQueryResult<Key>;
 
     fn no_op() -> Self;
+    fn is_no_op(&self) -> bool;
+    fn is_reinitialization(&self) -> bool;
     fn apply(&self, result: &mut Self::Result, range: &Range<Key>);
     fn compose(later: &Self, earlier: &mut Self);
 }

libs/persistent_range_query/src/ops/rsq.rs

@@ -76,6 +76,20 @@ where
         AddAssignModification::None
     }
 
+    fn is_no_op(&self) -> bool {
+        match self {
+            AddAssignModification::None => true,
+            _ => false,
+        }
+    }
+
+    fn is_reinitialization(&self) -> bool {
+        match self {
+            AddAssignModification::Assign(_) => true,
+            _ => false,
+        }
+    }
+
     fn apply<'a>(&self, result: &'a mut SumResult<T>, range: &Range<Key>) {
         use AddAssignModification::*;
         match self {