added Fetch method to get + set on miss

app/ccache.go

@@ -1,30 +0,0 @@
-package main
-
-import (
-  "fmt"
-  "time"
-  "ccache"
-)
-
-func main() {
-  c := ccache.New(ccache.Configure().PromoteDelay(time.Second * 0))
-  fmt.Println(c.Get("abc"))
-  c.Set("abc", new("xxx"))
-  fmt.Println(c.Get("abc"))
-  time.Sleep(time.Second)
-  fmt.Println(c.Get("abc"))
-  time.Sleep(time.Second)
-}
-
-type Item struct {
-  value string
-  expires time.Time
-}
-
-func (i *Item) Expires() time.Time {
-  return i.expires
-}
-
-func new(value string) *Item {
-  return &Item{value, time.Now().Add(time.Minute)}
-}

cache.go

@@ -51,6 +51,14 @@ func (c *Cache) Set(key string, value interface{}, duration time.Duration) {
   c.promote(item)
 }
 
+func (c *Cache) Fetch(key string, duration time.Duration, fetch func() interface{}) interface{} {
+  item := c.Get(key)
+  if item != nil { return item }
+  value := fetch()
+  c.Set(key, value, duration)
+  return value
+}
+
 func (c *Cache) Delete(key string) {
   item := c.bucket(key).getAndDelete(key)
   if item != nil {