Repository: maypok86/otter (go)

Issue:
Add delete by func
I really like otter, but what do miss (in comparison to ristretto for example) is something similar to a tag option. I need it sometimes to invalidate a part of the cache, and an easy option (in my opinion at least) to implement this would be to add a function to delete a part of the the cache depending on a function.

This would go along something like this:

```go
// DeleteByFunc removes the association for this key from the cache if the selectFunc returns true.
func (bs baseCache[K, V]) DeleteByFunc(selectFunc func(key K, value V) bool) {
	// aggregate all keys to delete
	keysToDelete := make([]K, 0)
	bs.Range(func(key K, value V) bool {
		if selectFunc(key, value) {
	            keysToDelete = append(keysToDelete, key)
        	}
	        return true
	})
	
	for _, key := range keysToDelete {
        	bs.Delete(key)
	}
}
```

You probably need a mutex, but the general idea should be clear.

Any additional ideas are appreciated.

Pull request:
[#44] Add DeleteByFunc function
## Description

Added DeleteByFunc function.

## Related issue(s)

- Resolves #44

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#### Related changes (conditional)

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    - [x] If I added new functionality, I added tests covering it.
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    - [x] My changes doesn't break project license.

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Patch:
diff --git a/cache.go b/cache.go
index 812a4d3..23d66af 100644
--- a/cache.go
+++ b/cache.go
@@ -70,6 +70,11 @@ func (bs baseCache[K, V]) Delete(key K) {
 	bs.cache.Delete(key)
 }
 
+// DeleteByFunc removes the association for this key from the cache when the given function returns true.
+func (bs baseCache[K, V]) DeleteByFunc(f func(key K, value V) bool) {
+	bs.cache.DeleteByFunc(f)
+}
+
 // Range iterates over all items in the cache.
 //
 // Iteration stops early when the given function returns false.
diff --git a/internal/core/cache.go b/internal/core/cache.go
index d5f7c98..85c4e73 100644
--- a/internal/core/cache.go
+++ b/internal/core/cache.go
@@ -232,6 +232,22 @@ func (c *Cache[K, V]) Delete(key K) {
 	}
 }
 
+// DeleteByFunc removes the association for this key from the cache when the given function returns true.
+func (c *Cache[K, V]) DeleteByFunc(f func(key K, value V) bool) {
+	// TODO(maypok86): This function can be implemented more efficiently, if the performance of this implementation is not enough for you, then come with an issue :)
+	var keysToDelete []K
+	c.Range(func(key K, value V) bool {
+		if f(key, value) {
+			keysToDelete = append(keysToDelete, key)
+		}
+		return true
+	})
+
+	for _, key := range keysToDelete {
+		c.Delete(key)
+	}
+}
+
 func (c *Cache[K, V]) cleanup() {
 	expired := make([]*node.Node[K, V], 0, 128)
 	for {


Test patch:
diff --git a/cache_test.go b/cache_test.go
index ba8961d..7a280bf 100644
--- a/cache_test.go
+++ b/cache_test.go
@@ -182,6 +182,29 @@ func TestCache_SetWithTTL(t *testing.T) {
 	}
 }
 
+func TestBaseCache_DeleteByFunc(t *testing.T) {
+	size := 256
+	c, err := MustBuilder[int, int](size).WithTTL(time.Hour).Build()
+	if err != nil {
+		t.Fatalf("can not create builder: %v", err)
+	}
+
+	for i := 0; i < size; i++ {
+		c.Set(i, i)
+	}
+
+	c.DeleteByFunc(func(key int, value int) bool {
+		return key%2 == 1
+	})
+
+	c.Range(func(key int, value int) bool {
+		if key%2 == 1 {
+			t.Fatalf("key should be odd, but got: %d", key)
+		}
+		return true
+	})
+}
+
 func TestCache_Ratio(t *testing.T) {
 	c, err := MustBuilder[uint64, uint64](100).CollectStats().Build()
 	if err != nil {