What is mix and match?

Mix and match allows us to create a project in either Objective-C or Swift, and include code from either language. This feature is arguably one of the most important features that came out with Swift.

The reason why this feature is so important is that there are over a million apps written in Objective-C in Apple's App Store, and it would not be feasible for developers to spend the resources required for converting all of these apps from Objective-C to Swift. Without mix and match, the adaptation of the Swift language would be very slow. With mix and match, developers can begin to use Swift in any of their present apps that are written in Objective-C without having to convert the entire code base to Swift.