iGodric iGodric - 1 year ago 62
Swift Question

Self in protocol always need to be optional?


internal protocol PropertyProtocol {
var property: Self {

The only option I see to implement it, let us say in a class is

internal final class PropertyClass: PropertyProtocol {
let property: PropertyClass

internal init(otherOne pOtherOne: PropertyClass) {
self.property = pOtherOne

But then I do not see a possibility to use it.

let test: PropertyProtocol = PropertyProtocol(...) // hmm, how?

Does Self in a protocol property type declaration always have to be optional?

Answer Source

As a stored property, indeed it would have to be optional for you to create an instance, as each instance would require the stored property to be assigned during initialisation – leading to recursive behaviour. Therefore Self doesn't make too much sense as a stored property; it's really more designed to be used with methods or calculated properties.

Depending on what you're using this for (seems like a fairly hypothetical example), you could implement a calculated property like so:

protocol PropertyProtocol {
    var property : Self { get }

final class PropertyClass : PropertyProtocol {
    var property : PropertyClass {
        get {
            return // ...
        set {
            // ...

That way the class itself can manage the creation of the property when it's accessed, preventing the recursive behaviour of requiring it to be assigned during initialisation.