Before iOS 17, this code does not compile:

class AuthManager: ObservableObject {
    @Published var accessToken: String?
    @Published var refreshToken: String?
    @Published var isAuthenticated: Bool { // NOT ALLOWED TO BE PUBLISHED
        return accessToken != nil && refreshToken != nil
    }
    // initializers
}

Following the migration guide from Apple, which suggests to basically replace ObservableObject with Observable and remove all the @Published property wrappers. And afterwards the follow now compiles:

@Observable
class AuthManager {
    var accessToken: String?
    var refreshToken: String?
    var isAuthenticated: Bool {
        return accessToken != nil && refreshToken != nil
    }
}

And I can indeed use isAuthenticated as a published state variable. So how come? Since it's computed, how would SwiftUI determine whether if it's changed? And would this still work if the computation was non-trivial? e.g. computed using the result of an http request

they have different implementations under the hood presumably the old way just didnt handle this for technical reasons, limitations in combine perhaps