RangeQueryResult: do not require Clone and do not provide default combine/add implementations

libs/persistent_range_query/src/lib.rs

@@ -11,22 +11,14 @@ pub trait RangeQueryResult<Key>: Sized {
 
     // Contract: left_range.end == right_range.start
     // left_range.start == left_range.end == right_range.start == right_range.end is still possible
-    fn combine(left: &Self, left_range: &Range<Key>, right: &Self, right_range: &Range<Key>) -> Self
-    where
-        Self: Clone,
-    {
-        let mut left = left.clone();
-        Self::add(&mut left, left_range, right, right_range);
-        left
-    }
+    fn combine(
+        left: &Self,
+        left_range: &Range<Key>,
+        right: &Self,
+        right_range: &Range<Key>,
+    ) -> Self;
 
-    // TODO: does it work with non-Clone?
-    fn add(left: &mut Self, left_range: &Range<Key>, right: &Self, right_range: &Range<Key>)
-    where
-        Self: Clone,
-    {
-        *left = Self::combine(left, left_range, right, right_range);
-    }
+    fn add(left: &mut Self, left_range: &Range<Key>, right: &Self, right_range: &Range<Key>);
 }
 
 pub trait LazyRangeInitializer<Result: RangeQueryResult<Key>, Key> {

libs/persistent_range_query/src/ops/rsq.rs

@@ -3,7 +3,7 @@
 use crate::ops::SameElementsInitializer;
 use crate::{LazyRangeInitializer, RangeModification, RangeQueryResult};
 use std::borrow::Borrow;
-use std::ops::{AddAssign, Range};
+use std::ops::{Add, AddAssign, Range};
 
 // TODO: commutative Add
 
@@ -18,11 +18,25 @@ impl<T> SumResult<T> {
     }
 }
 
-impl<T: for<'a> AddAssign<&'a T> + From<u8>, Key> RangeQueryResult<Key> for SumResult<T> {
+impl<T: for<'a> AddAssign<&'a T> + From<u8>, Key> RangeQueryResult<Key> for SumResult<T>
+where
+    for<'a> &'a T: Add<&'a T, Output = T>,
+{
     fn new_for_empty_range() -> Self {
         SumResult { sum: 0.into() }
     }
 
+    fn combine(
+        left: &Self,
+        _left_range: &Range<Key>,
+        right: &Self,
+        _right_range: &Range<Key>,
+    ) -> Self {
+        SumResult {
+            sum: &left.sum + &right.sum,
+        }
+    }
+
     fn add(left: &mut Self, _left_range: &Range<Key>, right: &Self, _right_range: &Range<Key>) {
         left.sum += &right.sum
     }