Merge pull request #6 from villegasl/master

Use Cursor().Seek() in LastN method of the List datatype instead of manually getting to the desired position

simplebolt.go

@@ -174,26 +174,24 @@ func (l *List) LastN(n int) (results []string, err error) {
 		if bucket == nil {
 			return ErrBucketNotFound
 		}
-		var size int64
-		bucket.ForEach(func(_, _ []byte) error {
-			size++
-			return nil // Continue ForEach
-		})
-		if size < int64(n) {
+		c := bucket.Cursor()
+		sizeBytes, _ := c.Last()
+		size := binary.BigEndian.Uint64(sizeBytes)
+		if size < uint64(n) {
 			return errors.New("Too few items in list")
 		}
-		// Ok, fetch the n last items. startPos is counting from 0.
-		var (
-			startPos = size - int64(n)
-			i        int64
-		)
-		bucket.ForEach(func(_, value []byte) error {
-			if i >= startPos {
+		// Ok, fetch the n last items. startPos is counting from (size - n)+1.
+		// +1 because Seek() moves to a specific key.
+		// e.g. if the size of the list is, say, 50, and we want the last 4
+		// elements, say, from 47 to 50 inclusive, then the calculation would be like this:
+		// size = 50
+		// n = 4
+		// startPos = size - n // startPos = 46
+		// startPos += 1 // startPos = 47
+		startPos := byteID(size - uint64(n) + 1)
+		for key, value := c.Seek(startPos); key != nil; key, value = c.Next() {
 				results = append(results, string(value))
-			}
-			i++
-			return nil // Continue ForEach
-		})
+		}
 		return nil // Return from View function
 	})
 }