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Mastering Swift 4 - Fourth Edition by Jon Hoffman

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Structures versus classes

You may have noticed that in the object-oriented design we used classes, while in protocol-oriented design 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 ...

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