protocol AppModel: AnyObject {
    func method1(completion: (Int) -> Void)
    func method2(completion: (Int) -> Void)
    func method3(completion: (Int) -> Void)
    // ...
    func methodN(completion: (Int) -> Void)
}

class SpecificAppModel: AppModel {
    func method1(completion: (Int) -> Void) { /* ... */ }
    func method2(completion: (Int) -> Void) { /* ... */ }
    func method3(completion: (Int) -> Void) { /* ... */ }
    // ...
    func methodN(completion: (Int) -> Void) { /* ... */ }
}