add v3 compatible with simplelru

v2 had most of the required functions, so this change adds missing ones
to satisfy the simplelru interface.

To do that, RemoveOldest started returning parameters, unlike being void
as before.

Another behaviour change is that Get and Peek now return
the cached value in case it has already expired to be consistent with
the `simplelru` implementation.

Also, GetExpiration is added.

README.md

@@ -18,7 +18,7 @@ either using LRC or LRU eviction.
 run cache.DeleteExpired periodically using [time.Ticker](https://golang.org/pkg/time/#Ticker),
 advisable period is 1/2 of TTL.
 
-This cache is heavily inspired by [hashicorp/golang-lru](https://github.com/hashicorp/golang-lru) _simplelru_ implementation. Key differences are:
+This cache is heavily inspired by [hashicorp/golang-lru](https://github.com/hashicorp/golang-lru) _simplelru_ implementation. v3 implements `simplelru.LRUCache` interface, so if you use a subset of functions, so you can switch from `github.com/hashicorp/golang-lru/v2/simplelru` or `github.com/hashicorp/golang-lru/v2/expirable` without any changes in your code except for cache creation. Key differences are:
 
 - Support LRC (Least Recently Created) in addition to LRU and TTL-based eviction
 - Supports per-key TTL setting

v3/cache.go

@@ -23,16 +23,23 @@ import (
 type Cache[K comparable, V any] interface {
 	fmt.Stringer
 	options[K, V]
+	Add(key K, value V) bool
 	Set(key K, value V, ttl time.Duration)
 	Get(key K) (V, bool)
+	GetExpiration(key K) time.Time
+	GetOldest() (K, V, bool)
+	Contains(key K) (ok bool)
 	Peek(key K) (V, bool)
+	Values() []V
 	Keys() []K
 	Len() int
+	Remove(key K) bool
 	Invalidate(key K)
 	InvalidateFn(fn func(key K) bool)
-	RemoveOldest()
+	RemoveOldest() (K, V, bool)
 	DeleteExpired()
 	Purge()
+	Resize(int) int
 	Stat() Stats
 }
 
@@ -71,8 +78,22 @@ func NewCache[K comparable, V any]() Cache[K, V] {
 	}
 }
 
+// Add adds a value to the cache. Returns true if an eviction occurred.
+// Returns false if there was no eviction: the item was already in the cache,
+// or the size was not exceeded.
+func (c *cacheImpl[K, V]) Add(key K, value V) (evicted bool) {
+	return c.addWithTTL(key, value, c.ttl)
+}
+
 // Set key, ttl of 0 would use cache-wide TTL
 func (c *cacheImpl[K, V]) Set(key K, value V, ttl time.Duration) {
+	c.addWithTTL(key, value, ttl)
+}
+
+// Returns true if an eviction occurred.
+// Returns false if there was no eviction: the item was already in the cache,
+// or the size was not exceeded.
+func (c *cacheImpl[K, V]) addWithTTL(key K, value V, ttl time.Duration) (evicted bool) {
 	c.Lock()
 	defer c.Unlock()
 	now := time.Now()
@@ -85,7 +106,7 @@ func (c *cacheImpl[K, V]) Set(key K, value V, ttl time.Duration) {
 		c.evictList.MoveToFront(ent)
 		ent.Value.(*cacheItem[K, V]).value = value
 		ent.Value.(*cacheItem[K, V]).expiresAt = now.Add(ttl)
-		return
+		return false
 	}
 
 	// Add new item
@@ -94,15 +115,17 @@ func (c *cacheImpl[K, V]) Set(key K, value V, ttl time.Duration) {
 	c.items[key] = entry
 	c.stat.Added++
 
-	// Remove oldest entry if it is expired, only in case of non-default TTL.
+	// Remove the oldest entry if it is expired, only in case of non-default TTL.
 	if c.ttl != noEvictionTTL || ttl != noEvictionTTL {
 		c.removeOldestIfExpired()
 	}
 
+	evict := c.maxKeys > 0 && len(c.items) > c.maxKeys
 	// Verify size not exceeded
-	if c.maxKeys > 0 && len(c.items) > c.maxKeys {
+	if evict {
 		c.removeOldest()
 	}
+	return evict
 }
 
 // Get returns the key value if it's not expired
@@ -114,7 +137,7 @@ func (c *cacheImpl[K, V]) Get(key K) (V, bool) {
 		// Expired item check
 		if time.Now().After(ent.Value.(*cacheItem[K, V]).expiresAt) {
 			c.stat.Misses++
-			return def, false
+			return ent.Value.(*cacheItem[K, V]).value, false
 		}
 		if c.isLRU {
 			c.evictList.MoveToFront(ent)
@@ -126,6 +149,15 @@ func (c *cacheImpl[K, V]) Get(key K) (V, bool) {
 	return def, false
 }
 
+// Contains checks if a key is in the cache, without updating the recent-ness
+// or deleting it for being stale.
+func (c *cacheImpl[K, V]) Contains(key K) (ok bool) {
+	c.Lock()
+	defer c.Unlock()
+	_, ok = c.items[key]
+	return ok
+}
+
 // Peek returns the key value (or undefined if not found) without updating the "recently used"-ness of the key.
 // Works exactly the same as Get in case of LRC mode (default one).
 func (c *cacheImpl[K, V]) Peek(key K) (V, bool) {
@@ -136,7 +168,7 @@ func (c *cacheImpl[K, V]) Peek(key K) (V, bool) {
 		// Expired item check
 		if time.Now().After(ent.Value.(*cacheItem[K, V]).expiresAt) {
 			c.stat.Misses++
-			return def, false
+			return ent.Value.(*cacheItem[K, V]).value, false
 		}
 		c.stat.Hits++
 		return ent.Value.(*cacheItem[K, V]).value, true
@@ -145,20 +177,65 @@ func (c *cacheImpl[K, V]) Peek(key K) (V, bool) {
 	return def, false
 }
 
+// GetExpiration returns the expiration time of the key. Non-existing key returns zero time.
+func (c *cacheImpl[K, V]) GetExpiration(key K) time.Time {
+	c.Lock()
+	defer c.Unlock()
+	if ent, ok := c.items[key]; ok {
+		return ent.Value.(*cacheItem[K, V]).expiresAt
+	}
+	return time.Time{}
+}
+
 // Keys returns a slice of the keys in the cache, from oldest to newest.
 func (c *cacheImpl[K, V]) Keys() []K {
 	c.Lock()
 	defer c.Unlock()
 	return c.keys()
 }
 
+// Values returns a slice of the values in the cache, from oldest to newest.
+// Expired entries are filtered out.
+func (c *cacheImpl[K, V]) Values() []V {
+	c.Lock()
+	defer c.Unlock()
+	values := make([]V, 0, len(c.items))
+	now := time.Now()
+	for ent := c.evictList.Back(); ent != nil; ent = ent.Prev() {
+		if now.After(ent.Value.(*cacheItem[K, V]).expiresAt) {
+			continue
+		}
+		values = append(values, ent.Value.(*cacheItem[K, V]).value)
+	}
+	return values
+}
+
 // Len return count of items in cache, including expired
 func (c *cacheImpl[K, V]) Len() int {
 	c.Lock()
 	defer c.Unlock()
 	return c.evictList.Len()
 }
 
+// Resize changes the cache size. Size of 0 means unlimited.
+func (c *cacheImpl[K, V]) Resize(size int) int {
+	c.Lock()
+	defer c.Unlock()
+	if size <= 0 {
+		c.maxKeys = 0
+		return 0
+	}
+	diff := c.evictList.Len() - size
+	if diff < 0 {
+		diff = 0
+	}
+	for i := 0; i < diff; i++ {
+		c.removeOldest()
+	}
+	c.maxKeys = size
+	return diff
+}
+
 // Invalidate key (item) from the cache
 func (c *cacheImpl[K, V]) Invalidate(key K) {
 	c.Lock()
@@ -179,11 +256,37 @@ func (c *cacheImpl[K, V]) InvalidateFn(fn func(key K) bool) {
 	}
 }
 
-// RemoveOldest remove oldest element in the cache
-func (c *cacheImpl[K, V]) RemoveOldest() {
+// Remove removes the provided key from the cache, returning if the
+// key was contained.
+func (c *cacheImpl[K, V]) Remove(key K) bool {
+	c.Lock()
+	defer c.Unlock()
+	if ent, ok := c.items[key]; ok {
+		c.removeElement(ent)
+		return true
+	}
+	return false
+}
+
+// RemoveOldest remove the oldest element in the cache
+func (c *cacheImpl[K, V]) RemoveOldest() (key K, value V, ok bool) {
 	c.Lock()
 	defer c.Unlock()
-	c.removeOldest()
+	if ent := c.evictList.Back(); ent != nil {
+		c.removeElement(ent)
+		return ent.Value.(*cacheItem[K, V]).key, ent.Value.(*cacheItem[K, V]).value, true
+	}
+	return
+}
+
+// GetOldest returns the oldest entry
+func (c *cacheImpl[K, V]) GetOldest() (key K, value V, ok bool) {
+	c.Lock()
+	defer c.Unlock()
+	if ent := c.evictList.Back(); ent != nil {
+		return ent.Value.(*cacheItem[K, V]).key, ent.Value.(*cacheItem[K, V]).value, true
+	}
+	return
 }
 
 // DeleteExpired clears cache of expired items