There are two main points that Apple thought of when introducing Swift:
Apple understood that and took it very seriously while working on Swift. They made Swift work seamlessly with Objective-C and Cocoa. You can use all Objective-C code in Swift, and you can even use Swift in Objective-C.
It's very crucial to be able to use the Cocoa framework. All of the code that is written in Objective-C is available for use in Swift, both Apple frameworks and third-party libraries as well.
All the Cocoa frameworks written in Objective-C are available in Swift by default. You just need to import them and then use them. Swift ...