Add storage ScanIterator trait

src/storage/engine/mod.rs

@@ -20,7 +20,7 @@ use serde::{Deserialize, Serialize};
 pub trait Engine: std::fmt::Display + Send + Sync {
  /// The iterator returned by scan(). Traits can't return "impl Trait", and
  /// we don't want to use trait objects, so the type must be specified.
- type ScanIterator<'a>: DoubleEndedIterator<Item = Result<(Vec<u8>, Vec<u8>)>> + 'a
+ type ScanIterator<'a>: ScanIterator + 'a
  where
  Self: 'a;
 
@@ -55,6 +55,11 @@ pub trait Engine: std::fmt::Display + Send + Sync {
  fn status(&mut self) -> Result<Status>;
 }
 
+/// A scan iterator, with a blanket implementation (in lieu of trait aliases).
+pub trait ScanIterator: DoubleEndedIterator<Item = Result<(Vec<u8>, Vec<u8>)>> {}
+
+impl<I: DoubleEndedIterator<Item = Result<(Vec<u8>, Vec<u8>)>>> ScanIterator for I {}
+
 /// Engine status.
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
 pub struct Status {