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Lesson 16 - Extensions and their use in Swift

In the previous lesson, Enums and custom errors in Swift, we learned how to use enumerated types and define custom error states in Swift.

Swift offers us the possibility to add functionality to existing data types, split a class implementation into multiple files or code blocks, and much more. That's what a powerful concept called extensions does. In today's tutorial, we'll show you how to add new methods to existing classes or structs (such as an ordinary Int), separate a protocol implementation and other tricks.

Extending existing types

This usage of extension is useful when we can’t edit some existing code. It can be either a part of the language like Int, String, etc. or, for example, a downloaded library. Perhaps the most useful feature is to add new methods to classes that aren't even ours and we have no access to them or don't want to interfere with them.


For example, consider we


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We'll explain what are extensions in Swift and show how to use them to extend our code and make it more readable.

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