Why would we use extensions to a protocol?

Question

I've just learned about extensions and I was wondering, there was an example about extending a protocol. For example, let's say we have the protocol:

protocol CanFly {
    func canFly()
}

which allows all the classes who can fly to basiclly to fly. Now lets say that we use extension to extend the protocol, and we do:

extension CanFly {
    func canEat() {
        print("I can eat")
    }
}

What is the purpose of that if we can just add that func canEat to our protocol? More of those protocols are like an abstract struct so why would we add a func with a body to it?

• just wanna say if I've made a mess im sorry for that lol, just want to clear out few things about extension <3

Answer 1

Per Swift documentation on Protocol Extensions:

Protocols can be extended to provide method, initializer, subscript, and computed property implementations to conforming types. This allows you to define behavior on protocols themselves, rather than in each type’s individual conformance or in a global function.

This means you can run logic within the protocol extension function so you don't have to do it in each class that conforms to the protocol.

Personally, I also find extensions useful to extend the functionality of built-in classes like String or UIViewController since extensions can be called from anywhere in an app. I have some open-source extension snippets you can take a look at if you'd like.