Make your User Default TypeSafe.

TypeSafeUserDefault.swift

import Foundation

// UserDefault is threadsafe
// https://developer.apple.com/documentation/foundation/userdefaults

struct State<T>: Equatable where T: Codable & Equatable {
    fileprivate let id: String
    fileprivate let `default`: T
}

extension State {
    static var isFirstTime: State<Bool> {
        return .init(id: "isFirstTime", default: true) }
}

class AppState {
    private init() {}
    
    static func get<T>(_ state: State<T>) -> T {
        let value = UserDefaults.standard.value(forKey: state.id) as? T
        return value ?? state.default
    }
    
    static func set<T>(_ state: State<T>, newValue: T) {
        UserDefaults.standard.set(newValue, forKey: state.id)
    }
}

#if DEBUG
// MARK: Usage

func usage() {
    if AppState.get(.isFirstTime) {
        print("Login")
    } else {
        print("Dashboard")
    }
}
#endif