Cannot use Protocols in SwiftUI Views

Question

I'm currently working on an App to manage Assignments, as I'm using different Types of Assignments like a To Do or a Homework, ... . So I made a Protocol for all key variables every Assignment should have, so that I can later display all different Types(conforming to Assignment) in one "All" List.

When testing in a Playground I managed to build a View which takes all Types conforming to Assignment and display title and description. But when starting in my main project I encountered these problems. Project Structure

a class Assignments holds all my data. Currently I have two lists with two types conforming to Assignment, HomeWork and OnlineLesson. This is just a transition and not good practise still...

a func getAll later should return both of those lists.

  class Assignments: Storable, Codable, ObservableObject {

      @Published var homeWorks: [HomeWork] 
      @Published var sortDescriptor: SortType
      @Published var onlineLessons: [OnlineLesson] 

     func getAll<A: Assignment>() -> [A] {
         var toReturn: [A] = []
     
         toReturn.append(contentsOf: homeWorks as! [A])
         toReturn.append(contentsOf: onlineLessons as! [A])
         //I also don't understand why I have to cast the arrays as both types already conform to Assignment

        return toReturn
     }
 }

This is the 'Assignment' protocol :

protocol Assignment: ObservableObject, Identifiable {
    var title: String {get set}
    var description: String {get set}
    var createdAt: Date {get}
    var dueTo: Date {get}
    var type: AssignmentType {get set}
}

The View

struct AssignmentsAllView: View {
    @EnvironmentObject var assignments: Assignments
    ...
}

@main
struct Homework_PlannerApp: App {
   var assignments: Assignments = Assignments()

   var body: some Scene {
       WindowGroup {
           ContentView()
               .environmentObject(assignments)
       }
   }
}

1st : Inside a List

ForEach(assigments.getAll()) {assigment in
    //Unable to infer type of a closure parameter 'assigment' in the current context
    // Generic parameter 'A' could not be inferred             
}

2nd : When trying it without a list

 Text(homeWorks.getAll().first!.title) //Generic parameter 'A' could not be inffered

Does someone know what I'm doing wrong, or how to fix this. As I'm new to protocols and I haven't enjoyed it so far to be honest.

Answer 1

Thanks for the Help, I got everything working by replacing the protocol Assignment, with an class Assignment:

class Assignment: ObservableObject {
    @Published var title: String
    @Published var description: String
    @Published var createdAt: Date
    @Published var dueTo: Date
    let type: AssigmentType
    
    init(title: String, description: String, dueTo: Date, type: AssigmentType) {
        self.title = title
        self.description = description
        self.createdAt = Date()
        self.dueTo = dueTo
        self.type = type
    }
}

The classes HomeWork and OnlineLesson now inherit from this super class...