Use flyweight for DataRowReader

conn.go

@@ -64,6 +64,7 @@ type Conn struct {
 	alive              bool
 	causeOfDeath       error
 	logger             log.Logger
+	drr                DataRowReader
 }
 
 type PreparedStatement struct {
@@ -328,10 +329,16 @@ func (c *Conn) selectFunc(sql string, onDataRow func(*DataRowReader) error, argu
 			fields = c.rxRowDescription(r)
 		case dataRow:
 			if softErr == nil {
-				var drr *DataRowReader
+				c.drr.mr = r
-				drr, softErr = newDataRowReader(r, fields)
+				c.drr.FieldDescriptions = fields
+				c.drr.currentFieldIdx = 0
+
+				fieldCount := int(r.ReadInt16())
+				if fieldCount != len(fields) {
+					softErr = ProtocolError(fmt.Sprintf("Row description field count (%v) and data row field count (%v) do not match", len(fields), fieldCount))
+				}
 				if softErr == nil {
-					softErr = onDataRow(drr)
+					softErr = onDataRow(&c.drr)
 				}
 			}
 		case commandComplete:

data_row_reader.go

@@ -11,19 +11,6 @@ type DataRowReader struct {
 	currentFieldIdx   int
 }
 
-func newDataRowReader(mr *MessageReader, fields []FieldDescription) (r *DataRowReader, err error) {
-	r = new(DataRowReader)
-	r.mr = mr
-	r.FieldDescriptions = fields
-
-	fieldCount := int(mr.ReadInt16())
-	if fieldCount != len(fields) {
-		return nil, ProtocolError(fmt.Sprintf("Row description field count (%v) and data row field count (%v) do not match", len(fields), fieldCount))
-	}
-
-	return
-}
-
 // ReadValue returns the next value from the current row.
 func (r *DataRowReader) ReadValue() interface{} {
 	fieldDescription := r.FieldDescriptions[r.currentFieldIdx]