FnMut instead of Fn

shardtree/src/store.rs

@@ -120,7 +120,7 @@ pub trait ShardStore {
     /// essentially the immutable version of `with_checkpoints`.
     fn for_each_checkpoint<F>(&self, limit: usize, callback: F) -> Result<(), Self::Error>
     where
-        F: Fn(&Self::CheckpointId, &Checkpoint) -> Result<(), Self::Error>;
+        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.
@@ -226,7 +226,7 @@ impl<S: ShardStore> ShardStore for &mut S {
 
     fn for_each_checkpoint<F>(&self, limit: usize, callback: F) -> Result<(), Self::Error>
     where
-        F: Fn(&Self::CheckpointId, &Checkpoint) -> Result<(), Self::Error>,
+        F: FnMut(&Self::CheckpointId, &Checkpoint) -> Result<(), Self::Error>,
     {
         S::for_each_checkpoint(self, limit, callback)
     }

shardtree/src/store/caching.rs

@@ -186,7 +186,7 @@ where
     }
     fn for_each_checkpoint<F>(&self, limit: usize, callback: F) -> Result<(), Self::Error>
     where
-        F: Fn(&Self::CheckpointId, &Checkpoint) -> Result<(), Self::Error>,
+        F: FnMut(&Self::CheckpointId, &Checkpoint) -> Result<(), Self::Error>,
     {
         self.cache.for_each_checkpoint(limit, callback)
     }

shardtree/src/store/memory.rs

@@ -137,9 +137,9 @@ impl<H: Clone, C: Clone + Ord> ShardStore for MemoryShardStore<H, C> {
         Ok(())
     }
 
-    fn for_each_checkpoint<F>(&self, limit: usize, callback: F) -> Result<(), Self::Error>
+    fn for_each_checkpoint<F>(&self, limit: usize, mut callback: F) -> Result<(), Self::Error>
     where
-        F: Fn(&C, &Checkpoint) -> Result<(), Self::Error>,
+        F: FnMut(&C, &Checkpoint) -> Result<(), Self::Error>,
     {
         for (cid, checkpoint) in self.checkpoints.iter().take(limit) {
             callback(cid, checkpoint)?