Once you’ve made the decision to move to a Swift code base, you don’t have to do it all at once. In fact, it’s perfectly fine to leave some parts of your app in Objective-C.
Think of the migration as a marathon, not a sprint. You want to make sure you do it right. You want to make sure that you finish it with a healthy code base.
Small, Focused Changes
As with most challenges in software development, it’s much easier to take it one step at a time. Converting an entire code base at once can leave a lot on your hands to deal with. Rather do your conversion in small, focused increments. Make a change, test that the project still works, and then repeat.
What Should I Leave in Objective-C?
You won’t be able to convert your third-party Objective-C libraries to Swift, and there’s nothing wrong with that. Xcode offers great interoperability between Objective-C and Swift.