make triedbmut lookup shorter

util/src/trie/triedbmut.rs

@@ -370,64 +370,49 @@ impl<'a> TrieDBMut<'a> {
 	fn lookup<'x, 'key>(&'x self, mut partial: NibbleSlice<'key>, handle: &NodeHandle) -> super::Result<Option<DBValue>>
 		where 'x: 'key
 	{
-		enum Step<'s> {
-			Return(Option<DBValue>),
-			Lookup(usize, &'s NodeHandle),
-		}
-
 		let mut handle = handle;
 		loop {
-			let step = {
-				match *handle {
-					NodeHandle::Hash(ref hash) => {
-						let lookup = Lookup {
+			let (mid, child) = match *handle {
+				NodeHandle::Hash(ref hash) => return Lookup {
 					db: &*self.db,
 					query: DBValue::from_slice,
 					hash: hash.clone(),
-						}.look_up(partial)?;
-						Step::Return(lookup)
-					},
+				}.look_up(partial),
 				NodeHandle::InMemory(ref handle) => match self.storage[handle] {
-						Node::Empty => Step::Return(None),
+					Node::Empty => return Ok(None),
 					Node::Leaf(ref key, ref value) => {
 						if NibbleSlice::from_encoded(key).0 == partial {
-								Step::Return(Some(DBValue::from_slice(value)))
+							return Ok(Some(DBValue::from_slice(value)));
 						} else {
-								Step::Return(None)
+							return Ok(None);
 						}
 					}
 					Node::Extension(ref slice, ref child) => {
 						let slice = NibbleSlice::from_encoded(slice).0;
 						if partial.starts_with(&slice) {
-								Step::Lookup(slice.len(), child)
+							(slice.len(), child)
 						} else {
-								Step::Return(None)
+							return Ok(None);
 						}
 					}
 					Node::Branch(ref children, ref value) => {
 						if partial.is_empty() {
-								Step::Return(value.as_ref().map(|v| DBValue::from_slice(v)))
+							return Ok(value.as_ref().map(|v| DBValue::from_slice(v)));
 						} else {
 							let idx = partial.at(0);
 							match children[idx as usize].as_ref() {
-									Some(child) => Step::Lookup(1, child),
-									None => Step::Return(None),
-								}
+								Some(child) => (1, child),
+								None => return Ok(None),
 							}
 						}
 					}
 				}
 			};
 
-			match step {
-				Step::Return(r) => return Ok(r),
-				Step::Lookup(mid, child) => {
 			partial = partial.mid(mid);
 			handle = child;
 		}
 	}
-		}
-	}
 
 	/// insert a key, value pair into the trie, creating new nodes if necessary.
 	fn insert_at(&mut self, handle: NodeHandle, partial: NibbleSlice, value: DBValue, old_val: &mut Option<DBValue>)