feat: bounded reverse iteration

packages/storey/src/containers/column.rs

@@ -457,7 +457,7 @@ pub enum LenError {
 
 #[cfg(test)]
 mod tests {
-    use crate::containers::RevIterableAccessor as _;
+    use crate::containers::{BoundedRevIterableAccessor as _, RevIterableAccessor as _};
 
     use super::*;
 
@@ -657,4 +657,51 @@ mod tests {
             vec![1337, 42, 1]
         );
     }
+
+    #[test]
+    fn bounded_rev_iteration() {
+        let mut storage = TestStorage::new();
+
+        let column = Column::<u64, TestEncoding>::new(0);
+        let mut access = column.access(&mut storage);
+
+        access.push(&1337).unwrap();
+        access.push(&42).unwrap();
+        access.push(&9001).unwrap();
+        access.push(&1).unwrap();
+        access.push(&2).unwrap();
+        access.remove(2).unwrap();
+
+        // start and end set
+        assert_eq!(
+            access
+                .bounded_rev_pairs(Some(1), Some(4))
+                .collect::<Result<Vec<_>, _>>()
+                .unwrap(),
+            vec![(3, 1), (1, 42)]
+        );
+        assert_eq!(
+            access
+                .bounded_rev_keys(Some(1), Some(4))
+                .collect::<Result<Vec<_>, _>>()
+                .unwrap(),
+            vec![3, 1]
+        );
+        assert_eq!(
+            access
+                .bounded_rev_values(Some(1), Some(4))
+                .collect::<Result<Vec<_>, _>>()
+                .unwrap(),
+            vec![1, 42]
+        );
+
+        // end unset
+        assert_eq!(
+            access
+                .bounded_rev_pairs(Some(1), None)
+                .collect::<Result<Vec<_>, _>>()
+                .unwrap(),
+            vec![(4, 2), (3, 1), (1, 42)]
+        );
+    }
 }

packages/storey/src/containers/mod.rs

@@ -233,6 +233,82 @@ pub trait BoundedIterableAccessor: IterableAccessor {
     }
 }
 
+/// This trait extends [`BoundedIterableAccessor`] with methods for bounded reverse iteration.
+/// Not every iterable collection supports it, so this trait is separate.
+///
+/// Bounded reverse iteration allows the user to specify a start and end bound for the iteration,
+/// but in reverse order.
+///
+/// # Why not always support bounded reverse iteration?
+///
+/// The same reasons as for [bounded iteration](BoundedIterableAccessor) apply.
+pub trait BoundedRevIterableAccessor
+where
+    Self: BoundedIterableAccessor,
+    Self::Storage: RevIterableStorage,
+{
+    /// Iterate over key-value pairs in this collection in reverse order, respecting the given bounds.
+    fn bounded_rev_pairs<B>(
+        &self,
+        start: Option<B>,
+        end: Option<B>,
+    ) -> StorableIter<Self::Storable, <Self::Storage as RevIterableStorage>::RevPairsIterator<'_>>
+    where
+        B: BoundFor<Self::Storable>,
+    {
+        let start = start.map(|b| b.into_bytes());
+        let end = end.map(|b| b.into_bytes());
+
+        StorableIter {
+            inner: self.storage().rev_pairs(start.as_deref(), end.as_deref()),
+            phantom: PhantomData,
+        }
+    }
+
+    /// Iterate over keys in this collection in reverse order, respecting the given bounds.
+    fn bounded_rev_keys<B>(
+        &self,
+        start: Option<B>,
+        end: Option<B>,
+    ) -> StorableKeys<Self::Storable, <Self::Storage as RevIterableStorage>::RevKeysIterator<'_>>
+    where
+        B: BoundFor<Self::Storable>,
+    {
+        let start = start.map(|b| b.into_bytes());
+        let end = end.map(|b| b.into_bytes());
+
+        StorableKeys {
+            inner: self.storage().rev_keys(start.as_deref(), end.as_deref()),
+            phantom: PhantomData,
+        }
+    }
+
+    /// Iterate over values in this collection in reverse order, respecting the given bounds.
+    fn bounded_rev_values<B>(
+        &self,
+        start: Option<B>,
+        end: Option<B>,
+    ) -> StorableValues<Self::Storable, <Self::Storage as RevIterableStorage>::RevValuesIterator<'_>>
+    where
+        B: BoundFor<Self::Storable>,
+    {
+        let start = start.map(|b| b.into_bytes());
+        let end = end.map(|b| b.into_bytes());
+
+        StorableValues {
+            inner: self.storage().rev_values(start.as_deref(), end.as_deref()),
+            phantom: PhantomData,
+        }
+    }
+}
+
+impl<I> BoundedRevIterableAccessor for I
+where
+    I: BoundedIterableAccessor,
+    I::Storage: RevIterableStorage,
+{
+}
+
 /// A type that can be used as bounds for iteration over a given collection.
 ///
 /// As an example, a collection `Foo` with string-y keys can accept both `String` and