Immutable For Each on ShardStore Checkpoints

shardtree/src/store.rs

@@ -116,6 +116,12 @@ pub trait ShardStore {
     where
         F: FnMut(&Self::CheckpointId, &Checkpoint) -> Result<(), Self::Error>;
 
+    /// Calls the given callback for each checkpoint in `CheckpointId` order. This is
+    /// essentially the immutable version of `with_checkpoints`.
+    fn for_each_checkpoint<F>(&self, limit: usize, callback: F) -> Result<(), Self::Error>
+    where
+        F: FnMut(&Self::CheckpointId, &Checkpoint) -> Result<(), Self::Error>;
+
     /// Update the checkpoint having the given identifier by mutating it with the provided
     /// function, and persist the updated checkpoint to the data store.
     ///
@@ -218,6 +224,13 @@ impl<S: ShardStore> ShardStore for &mut S {
         S::with_checkpoints(self, limit, callback)
     }
 
+    fn for_each_checkpoint<F>(&self, limit: usize, callback: F) -> Result<(), Self::Error>
+    where
+        F: FnMut(&Self::CheckpointId, &Checkpoint) -> Result<(), Self::Error>,
+    {
+        S::for_each_checkpoint(self, limit, callback)
+    }
+
     fn update_checkpoint_with<F>(
         &mut self,
         checkpoint_id: &Self::CheckpointId,

shardtree/src/store/caching.rs

@@ -184,6 +184,12 @@ where
     {
         self.cache.with_checkpoints(limit, callback)
     }
+    fn for_each_checkpoint<F>(&self, limit: usize, callback: F) -> Result<(), Self::Error>
+    where
+        F: FnMut(&Self::CheckpointId, &Checkpoint) -> Result<(), Self::Error>,
+    {
+        self.cache.for_each_checkpoint(limit, callback)
+    }
 
     fn update_checkpoint_with<F>(
         &mut self,

shardtree/src/store/memory.rs

@@ -137,6 +137,17 @@ impl<H: Clone, C: Clone + Ord> ShardStore for MemoryShardStore<H, C> {
         Ok(())
     }
 
+    fn for_each_checkpoint<F>(&self, limit: usize, mut callback: F) -> Result<(), Self::Error>
+    where
+        F: FnMut(&C, &Checkpoint) -> Result<(), Self::Error>,
+    {
+        for (cid, checkpoint) in self.checkpoints.iter().take(limit) {
+            callback(cid, checkpoint)?
+        }
+
+        Ok(())
+    }
+
     fn update_checkpoint_with<F>(
         &mut self,
         checkpoint_id: &C,