diff --git a/src/key.rs b/src/key.rs
index 1114070..0c6dfa9 100644
--- a/src/key.rs
+++ b/src/key.rs
@@ -9,12 +9,12 @@ use std::marker::PhantomData;
 /// a key from a value that is Hash.
 ///
 #[derive(Clone)]
-pub struct S3FIFOKey<V: Hash> {
+pub struct S3FIFOKey<V> {
     hash: u64,
     _phantom: PhantomData<V>,
 }
 
-impl<V: Hash> PartialEq for S3FIFOKey<V> {
+impl<V> PartialEq for S3FIFOKey<V> {
     fn eq(&self, other: &Self) -> bool {
         self.hash == other.hash
     }
@@ -36,7 +36,7 @@ impl<V: Hash> S3FIFOKey<V> {
     }
 }
 
-impl<V: Hash> std::fmt::Debug for S3FIFOKey<V> {
+impl<V> std::fmt::Debug for S3FIFOKey<V> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         f.debug_struct("S3FIFOKey")
             .field("hash", &self.hash)
@@ -44,8 +44,8 @@ impl<V: Hash> std::fmt::Debug for S3FIFOKey<V> {
     }
 }
 
-impl<V: Hash> Display for S3FIFOKey<V> {
+impl<V> Display for S3FIFOKey<V> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         write!(f, "{:#x}", self.hash)
     }
-}
\ No newline at end of file
+}
diff --git a/src/lib.rs b/src/lib.rs
index 013d761..703c384 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -3,6 +3,7 @@
 
 use std::{
     collections::VecDeque,
+    fmt::{self, Debug},
     sync::atomic::{AtomicI8, Ordering},
 };
 
@@ -42,6 +43,19 @@ pub struct S3FIFO<K, V> {
     main: VecDeque<Item<K, V>>,
     ghost: VecDeque<Key<K>>,
 }
+impl<K, V> std::fmt::Debug for S3FIFO<K, V>
+where
+    K: std::fmt::Debug,
+    V: std::fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("S3FIFO")
+            .field("small", &self.small)
+            .field("main", &self.main)
+            .field("ghost", &self.ghost)
+            .finish()
+    }
+}
 
 impl<K: PartialEq + Clone, V> S3FIFO<K, V> {
     ///
@@ -155,7 +169,7 @@ impl<K: PartialEq + Clone, V> S3FIFO<K, V> {
                 evicted = self.evict_main();
             }
             self.main.push_front(item);
-            return (&mut self.main.front_mut().unwrap().value, evicted);
+            (&mut self.main.front_mut().unwrap().value, evicted)
         } else {
             let item = Item {
                 key,
@@ -166,7 +180,7 @@ impl<K: PartialEq + Clone, V> S3FIFO<K, V> {
                 evicted = self.evict_small();
             }
             self.small.push_front(item);
-            return (&mut self.small.front_mut().unwrap().value, evicted);
+            (&mut self.small.front_mut().unwrap().value, evicted)
         }
     }
 
@@ -220,9 +234,7 @@ impl<K: PartialEq + Clone, V> S3FIFO<K, V> {
         // then the maximum number of iterations is 3 * main.len() + 1
         let mut iters = (3 * self.main.len() + 1) as isize;
         while iters > 0 {
-            let Some(item) = self.main.pop_back() else {
-                return None;
-            };
+            let item = self.main.pop_back()?;
             iters -= 1;
             let freq = item.freq.load(Ordering::Relaxed);
             if freq > 0 {
@@ -242,11 +254,37 @@ struct Item<K, V> {
     freq: AtomicI8, // not thread-safe
 }
 
+impl<K, V> Debug for Item<K, V>
+where
+    K: Debug,
+    V: Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Item")
+            .field("key", &self.key)
+            .field("value", &self.value)
+            .field("freq", &self.freq)
+            .finish()
+    }
+}
+
 struct Key<K> {
     key: K,
     freq: AtomicI8, // not thread-safe
 }
 
+impl<K> Debug for Key<K>
+where
+    K: Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Key")
+            .field("key", &self.key)
+            .field("freq", &self.freq)
+            .finish()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;