Should I define computed property of inside of protocol if the extension with implementation follows?

Question

What's the difference between:

protocol DashboardTargetInfo: TargetInfo {
    var apiVersion: Int { get }
}

extension DashboardTargetInfo {
    var apiVersion: Int {
        5
    }
}

And the one without computed property included in protocol definition

protocol DashboardTargetInfo: TargetInfo {}

extension DashboardTargetInfo {
    
    var apiVersion: Int {
        5
    }
}

Should I include the definition of the computed "apiVersion" property if the extension definition is following? Is there any difference between those two snippets of code?

Answer 1

In the first version apiVersion is part of the protocol and any conforming types must implement the property or use the default one. In the second one this is just a computed property that is available for types conforming to it and not part of the protocol.

An example:

struct Test1: DashboardTargetInfo { var apiVersion: Int }
struct Test2: DashboardTargetInfo { var apiVersion: Int { 10 } }

let values: [DashboardTargetInfo] = [Test1(apiVersion: 42), Test2()]
print(values.map(\.apiVersion))

With the first version of the protocol we get the values of the conforming types

[42, 10]

But if our types conforms to the second example then apiVersion is not part of the protocol so only the default computed value is used

[5, 5]