Apple now allows developers to create unified purchases across Mac and iOS, enabling a user to buy an app on one platform and use it on another.
The change means that a developer can list an iPad app in the App Store and a Mac version in the Mac App Store, using Apple's Catalyst technology. If a customer buys one version, it automatically unlocks the app for all available platforms.
There are some caveats for developers, though. The default is a Mac and iOS bundle. Existing versions of independent Mac and iOS applications cannot be combined at this point. In-app purchases can be shared across platforms as well.
The update came with the new Xcode 11.4 beta, and developers will need to change existing apps' bundle identifiers if they intend to sell them as unified purchases.
The feature will be quite useful for developers creating macOS ports of iOS apps with Catalyst. Catalyst allows iOS app developers to select one extra option within Apple's Xcode and have a Mac app generated automatically — but it won't be optimized for the Mac in any real way. By way of example, in 2018, Apple released macOS versions of its own News, Stocks, Home and Voice Memos apps, and has refined them in macOS Catalina.
Developer responses to Catalyst have been somewhat split. Some developers have no use for Catalyst, as they've already got Mac apps, either released or in development. For others, though, Catalyst is the reason they began considering making a Mac version of their iOS and iPadOS apps.