Protocol Extension in Swift Where Object Is a Class and conforms to a Protocol

Question

I have two protocols (Archivable and Serializable) and a class (Model) that is subclassed multiple times. Many of the subclasses implement either Archivable or Serializable (or both). I'd like to define a function on all children of Model that implement both Archivable and Serializable. Both of these work:

extension Serializable where Self: Model {   func fetch() { ... } } 

or

extension Serializable where Self: Archivable {   func fetch() { ... } } 

However I can't figure out how to extend where both protocols are required. Are there any other options outside of creating a third protocol that conforms to the first two?

Answer 1

I think this should work:

extension Archivable where Self: Model, Self: Serializable {      func fetch() { ... }  } 

... or the other way around:

extension Serializable where Self: Model, Self: Archivable {      func fetch() { ... }  } 

Answer 2

You can use a composition of protocols

extension Serializable where Self: Model & Archivable {     func fetch() { ... } }