feat: add GetNewest() to get head entry from lru list

lru.go

@@ -225,6 +225,14 @@ func (c *Cache[K, V]) GetOldest() (key K, value V, ok bool) {
 	return
 }
 
+// GetNewest returns the oldest entry
+func (c *Cache[K, V]) GetNewest() (key K, value V, ok bool) {
+	c.lock.RLock()
+	key, value, ok = c.lru.GetNewest()
+	c.lock.RUnlock()
+	return
+}
+
 // Keys returns a slice of the keys in the cache, from oldest to newest.
 func (c *Cache[K, V]) Keys() []K {
 	c.lock.RLock()

simplelru/list.go

@@ -61,6 +61,14 @@ func (l *lruList[K, V]) back() *entry[K, V] {
 	return l.root.prev
 }
 
+// head returns the first element of list l or nil if the list is empty.
+func (l *lruList[K, V]) head() *entry[K, V] {
+	if l.len == 0 {
+		return nil
+	}
+	return l.root.next
+}
+
 // lazyInit lazily initializes a zero List value.
 func (l *lruList[K, V]) lazyInit() {
 	if l.root.next == nil {

simplelru/lru.go

@@ -121,6 +121,14 @@ func (c *LRU[K, V]) GetOldest() (key K, value V, ok bool) {
 	return
 }
 
+// GetNewest returns the newest entry
+func (c *LRU[K, V]) GetNewest() (key K, value V, ok bool) {
+	if ent := c.evictList.head(); ent != nil {
+		return ent.key, ent.value, true
+	}
+	return
+}
+
 // Keys returns a slice of the keys in the cache, from oldest to newest.
 func (c *LRU[K, V]) Keys() []K {
 	keys := make([]K, c.evictList.length())

simplelru/lru_interface.go

@@ -29,6 +29,9 @@ type LRUCache[K comparable, V any] interface {
 	// Returns the oldest entry from the cache. #key, value, isFound
 	GetOldest() (K, V, bool)
 
+	// Returns the newest entry from the cache. #key, value, isFound
+	GetNewest() (K, V, bool)
+
 	// Returns a slice of the keys in the cache, from oldest to newest.
 	Keys() []K
 

simplelru/lru_test.go

@@ -111,6 +111,44 @@ func TestLRU_GetOldest_RemoveOldest(t *testing.T) {
 	}
 }
 
+func TestLRU_GetNewest(t *testing.T) {
+	l, err := NewLRU[int, int](128, nil)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	for i := 0; i < 256; i++ {
+		l.Add(i, i)
+	}
+
+	k, _, ok := l.GetOldest()
+	if !ok {
+		t.Fatalf("missing")
+	}
+	if k != 128 {
+		t.Fatalf("bad oldest: %v", k)
+	}
+
+	k, _, ok = l.GetNewest()
+	if !ok {
+		t.Fatalf("missing")
+	}
+	if k != 255 {
+		t.Fatalf("bad newest: %v", k)
+	}
+
+	l.Get(128)
+	k, _, _ = l.GetNewest()
+	if k != 128 {
+		t.Fatalf("bad newest: %v", k)
+	}
+
+	l.Get(200)
+	k, _, _ = l.GetNewest()
+	if k != 200 {
+		t.Fatalf("bad newest: %v", k)
+	}
+}
+
 // Test that Add returns true/false if an eviction occurred
 func TestLRU_Add(t *testing.T) {
 	evictCounter := 0