no need to check the driver implements the watcher interface.

shogo82148 · shogo82148 · commit ccd26221cb6a · 2018-04-07T15:48:34.000+09:00
because Connector.Connect is built with Go1.10 or higher.
diff --git a/connector.go b/connector.go
@@ -58,9 +58,7 @@ func (c Connector) Connect(ctx context.Context) (driver.Conn, error) {
 	}
 
 	// Call startWatcher for context support (From Go 1.8)
-	if s, ok := interface{}(mc).(watcher); ok {
-		s.startWatcher()
-	}
+	mc.startWatcher()
 	if err := mc.watchCancel(ctx); err != nil {
 		return nil, err
 	}

Original file line number	Diff line number	Diff line change
`@@ -58,9 +58,7 @@ func (c Connector) Connect(ctx context.Context) (driver.Conn, error) {`
`58`	`58`	`}`
`59`	`59`
`60`	`60`	`// Call startWatcher for context support (From Go 1.8)`
`61`		`- if s, ok := interface{}(mc).(watcher); ok {`
`62`		`- s.startWatcher()`
`63`		`- }`
	`61`	`+ mc.startWatcher()`
`64`	`62`	`if err := mc.watchCancel(ctx); err != nil {`
`65`	`63`	`return nil, err`
`66`	`64`	`}`