Adding support for OnDelete callback function

OnDelete will receive an item that is being processed for deletion to support calling cleanup function specific to the item stored

cache.go

@@ -186,6 +186,9 @@ func (c *Cache) doDelete(item *Item) {
 		item.promotions = -2
 	} else {
 		c.size -= item.size
+		if c.onDelete != nil {
+			c.onDelete(item)
+		}
 		c.list.Remove(item.element)
 	}
 }

cache_test.go

@@ -23,6 +23,28 @@ func (_ CacheTests) DeletesAValue() {
 	Expect(cache.Get("worm").Value()).To.Equal("sand")
 }
 
+func (_ CacheTests) OnDeleteCallbackCalled() {
+
+	onDeleteFnCalled := false
+	onDeleteFn := func(item *Item) {
+		if item.key == "spice" {
+			onDeleteFnCalled = true
+		}
+	}
+
+	cache := New(Configure().OnDelete(onDeleteFn))
+	cache.Set("spice", "flow", time.Minute)
+	cache.Set("worm", "sand", time.Minute)
+
+	time.Sleep(time.Millisecond * 10) // Run once to init
+	cache.Delete("spice")
+	time.Sleep(time.Millisecond * 10) // Wait for worker to pick up deleted items
+
+	Expect(cache.Get("spice")).To.Equal(nil)
+	Expect(cache.Get("worm").Value()).To.Equal("sand")
+	Expect(onDeleteFnCalled).To.Equal(true)
+}
+
 func (_ CacheTests) FetchesExpiredItems() {
 	cache := New(Configure())
 	fn := func() (interface{}, error) { return "moo-moo", nil }

configuration.go

@@ -8,6 +8,7 @@ type Configuration struct {
 	promoteBuffer  int
 	getsPerPromote int32
 	tracking       bool
+	onDelete       func(item *Item)
 }
 
 // Creates a configuration object with sensible defaults
@@ -92,3 +93,11 @@ func (c *Configuration) Track() *Configuration {
 	c.tracking = true
 	return c
 }
+
+// OnDelete allows setting a callback function to react to ideam deletion.
+// This typically allows to do a cleanup of resources, such as calling a Close() on
+// cached object that require some kind of tear-down.
+func (c *Configuration) OnDelete(callback func(item *Item)) *Configuration {
+	c.onDelete = callback
+	return c
+}

layeredcache.go

@@ -195,6 +195,9 @@ func (c *LayeredCache) worker() {
 				item.promotions = -2
 			} else {
 				c.size -= item.size
+				if c.onDelete != nil {
+					c.onDelete(item)
+				}
 				c.list.Remove(item.element)
 			}
 		}

layeredcache_test.go

@@ -1,10 +1,11 @@
 package ccache
 
 import (
-	. "github.com/karlseguin/expect"
 	"strconv"
 	"testing"
 	"time"
+
+	. "github.com/karlseguin/expect"
 )
 
 type LayeredCacheTests struct{}
@@ -65,6 +66,33 @@ func (_ *LayeredCacheTests) DeletesAValue() {
 	Expect(cache.Get("leto", "sister").Value()).To.Equal("ghanima")
 }
 
+func (_ *LayeredCacheTests) OnDeleteCallbackCalled() {
+
+	onDeleteFnCalled := false
+	onDeleteFn := func(item *Item) {
+
+		if item.group == "spice" && item.key == "flow" {
+			onDeleteFnCalled = true
+		}
+	}
+
+	cache := Layered(Configure().OnDelete(onDeleteFn))
+	cache.Set("spice", "flow", "value-a", time.Minute)
+	cache.Set("spice", "must", "value-b", time.Minute)
+	cache.Set("leto", "sister", "ghanima", time.Minute)
+
+	time.Sleep(time.Millisecond * 10) // Run once to init
+	cache.Delete("spice", "flow")
+	time.Sleep(time.Millisecond * 10) // Wait for worker to pick up deleted items
+
+	Expect(cache.Get("spice", "flow")).To.Equal(nil)
+	Expect(cache.Get("spice", "must").Value()).To.Equal("value-b")
+	Expect(cache.Get("spice", "worm")).To.Equal(nil)
+	Expect(cache.Get("leto", "sister").Value()).To.Equal("ghanima")
+
+	Expect(onDeleteFnCalled).To.Equal(true)
+}
+
 func (_ *LayeredCacheTests) DeletesALayer() {
 	cache := newLayered()
 	cache.Set("spice", "flow", "value-a", time.Minute)