Swift is a new programming language that is purely compatible with objective C. This makes it possible to use objective C file code in Swift file. Apple claims the co-existence of Swift and Objective C in an application but, this does not relate to re-using old classes made in Objective-C whilst building new classes in Swift. The reason being as Objective-C is a platform-independent language unlike Swift is platform-dependent. Now, implementing non-platform-dependent code in Swift won’t be fruitful. henceforth, writing platform dependent code in Swift would be absolutely fine.