Скачать или смотреть Chapter 8. Protocols and Extensions: A Swift Lesson in Protocol - Part 1

Protocols let you describe a set of properties and methods that a struct or class must have.

A struct or class can adopt any number of protocols, requiring it to implement the properties and methods the protocols it adheres to describe.

Protocols are not used directly. They’re just descriptions of something that can be created.

A protocol can inherit from one or more other protocols. This is called protocol inheritance.

Extensions let you add features to types that you did not create.

Anything you add to a type with an extension is treated exactly the same way as if it was built into the original type.

Extensions can add methods and computed properties, but not stored properties.

Extensions are also useful for organizing your code. Separating your code and the features of a type you’ve created using extensions can help make your code easier to read and understand.