improved EntryNotFoundError (#92)

* EntryNotFound generate error message only if Error is executed

* added bench readFromCacheNonExistentKeys

bigcache_bench_test.go

@@ -98,6 +98,14 @@ func BenchmarkWriteToCacheWith1024ShardsAndSmallShardInitSize(b *testing.B) {
 	writeToCache(b, 1024, 100*time.Second, 100)
 }
 
+func BenchmarkReadFromCacheNonExistentKeys(b *testing.B) {
+	for _, shards := range []int{1, 512, 1024, 8192} {
+		b.Run(fmt.Sprintf("%d-shards", shards), func(b *testing.B) {
+			readFromCacheNonExistentKeys(b, 1024)
+		})
+	}
+}
+
 func writeToCache(b *testing.B, shards int, lifeWindow time.Duration, requestsInLifeWindow int) {
 	cache, _ := NewBigCache(Config{
 		Shards:             shards,
@@ -139,3 +147,21 @@ func readFromCache(b *testing.B, shards int) {
 		}
 	})
 }
+
+func readFromCacheNonExistentKeys(b *testing.B, shards int) {
+	cache, _ := NewBigCache(Config{
+		Shards:             shards,
+		LifeWindow:         1000 * time.Second,
+		MaxEntriesInWindow: max(b.N, 100),
+		MaxEntrySize:       500,
+	})
+	b.ResetTimer()
+
+	b.RunParallel(func(pb *testing.PB) {
+		b.ReportAllocs()
+
+		for pb.Next() {
+			cache.Get(strconv.Itoa(rand.Intn(b.N)))
+		}
+	})
+}

entry_not_found_error.go

@@ -4,14 +4,14 @@ import "fmt"
 
 // EntryNotFoundError is an error type struct which is returned when entry was not found for provided key
 type EntryNotFoundError struct {
-	message string
+	key string
 }
 
 func notFound(key string) error {
-	return &EntryNotFoundError{fmt.Sprintf("Entry %q not found", key)}
+	return &EntryNotFoundError{key}
 }
 
 // Error returned when entry does not exist.
 func (e EntryNotFoundError) Error() string {
-	return e.message
+	return fmt.Sprintf("Entry %q not found", e.key)
 }