Make clippy happy

Signed-off-by: Chojan Shang <psiace@outlook.com>

src/cache.rs

@@ -508,7 +508,7 @@ where
     /// }
     /// ```
     ///
-    pub fn insert(&mut self, k: K, v: V) -> Result<Option<V>, ()> {
+    pub fn insert(&mut self, k: K, v: V) -> Result<Option<V>, Option<()>> {
         self.insert_with_ttl(k, v, Duration::from_secs(0))
     }
 
@@ -538,7 +538,12 @@ where
     /// assert!(!cache.contains(&1));
     /// ```
     ///
-    pub fn insert_with_ttl(&mut self, k: K, v: V, expiration: Duration) -> Result<Option<V>, ()> {
+    pub fn insert_with_ttl(
+        &mut self,
+        k: K,
+        v: V,
+        expiration: Duration,
+    ) -> Result<Option<V>, Option<()>> {
         self.store.cleanup(&self.on_evict);
 
         let key_hash = self.key_hash(&k);
@@ -561,7 +566,7 @@ where
             }
             Err(victim) => {
                 self.remove_victim(victim);
-                Err(())
+                Err(Some(()))
             }
         }
     }

src/metrics.rs

@@ -104,6 +104,12 @@ impl Metrics {
     }
 }
 
+impl Default for Metrics {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl Debug for Metrics {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         f.debug_struct("Metrics")

src/tiny_lfu.rs

@@ -108,7 +108,7 @@ impl TinyLFU for TinyLFUCache {
         } else {
             self.sketcher.insert(k, 1);
             self.previous_window.remove(k);
-            self.actual_window.insert(k.clone());
+            self.actual_window.insert(*k);
         }
         self.increments += 1;
     }

src/ttl.rs

@@ -151,7 +151,7 @@ impl Expiration for ExpirationMap {
         let mut result = HashSet::new();
         let mut buckets = Vec::new();
         for (id, _) in self.buckets.range(..now) {
-            buckets.push(id.clone())
+            buckets.push(*id)
         }
         for bucket in buckets {
             for item in self.buckets.remove(&bucket).unwrap() {