MacRumors reports that Google has updated its Gmail for iOS app with several new features, including quick actions, a new attachment viewer, and a feature that lets you email files from other apps. The latter means that you now have the ability to attach photos and documents to Gmail via Instagram and many other picture or document apps via the updated in-app share sheet.
Quick actions is probably one of the most useful new features included in the update, as it enables you to archive or reply to emails directly from a notification without having to leave your current app. It also works in the Notification Center and Lock screen. Some users are complaining about the lack of an option to delete files rather than archive or reply to them, so that might be something Google could look at in a future update.
The new attachment viewer simply enables you to open Gmail attachments in any app.
Source: http://www.macrumors.com/2015/03/05/gmail-for-ios-version-4-0/