Protocol Extensions in Swift

Swift Protocol

01 May 2020 . 1 min read       @gurjitpt

A protocol can defines a set of methods that can be adopted by any class, but we can’t write code inside. On the other hand, extensions gives us the power to write code inside methods, but it can only used for one type.

In Protocol Extensions, we can extend protocols to provide implementations to all conforming types rather than extending a particular type.

For example, we have an array named oddNumbers contains odd numbers and a set named evenNumbers that contains even numbers.

let oddNumbers: [Int] = [1,5,23,91]
let evenNumbers: Set = [34,56,12,78,22]

Now, we have protocol Collection that can be extended to provide countItems() method which returns total numbers of items.

extension Collection {
    func countItems() -> Int {
         return count

Both conforming types gain countItems method by extending the protocol and prints total number of items available.


Protocol Extensions can’t extend or inherit from another protocol.

Don’t hesitate to contact me if you have any questions or queries. Follow me on twitter @gurjitpt for any updates.


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Gurjit Singh

I’m Computer Science graduate and an iOS Engineer who writes about Swift and iOS development. Follow me on twitter @gurjitpt for more updates.

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