Structures versus classes
You may have noticed that in the object-oriented design we used classes, while in the protocol-oriented design example we used structures. Classes, which are reference types, are one of the pillars of object-oriented programming and every major object-oriented programming language uses them. For Swift, Apple has said that we should prefer value types (structures) to reference types (classes). While this may seem odd for anyone who has extensive experience with object-oriented programming, there are several good reasons for this recommendation.
The biggest reason, in my opinion, for using structures (value types) over classes is the performance gain we get. Value types do not incur the additional overhead for reference counting that reference types incur. Value types are also stored on the stack, which provides better performance as compared to reference types, which are stored on the heap. It is also worth noting that copying values is relatively cheap...
