I am using Apollo for Swift in an iOS app. I have multiple types that all represent the same object. These types are auto-generated from a schema file and look something like this.
struct CurrentUser {
var id: String
...
}
struct MyUser {
var id: String
...
}
Basically Apollo generates multiple Swift types (one for each query) for the same underlying data type.
I want to create a new struct that unifies these types.
I would like to do something like this:
protocol UserProtocol {
var id: String { get }
}
struct User {
var id: String
...
init(_ data: UserProtocol) {
self.id = data.id
...
}
}
This approach however gives me an error when I try to construct a user object, telling me that "Type MyUser does not conform to UserProtocol". If I try to coerce the type with data as! UserProtocol I get a crash.
The only solution I've found is the following:
enum UserType {
case .currentUser(CurrentUser)
case .myUser(MyUser)
}
struct User {
var id: String
...
init(_ data: UserType) {
switch data {
case .myUser(let user):
self.id = data.id
...
case .currentUser(let user):
self.id = data.id
...
}
}
}
This approach works, but it leads to a lot of duplicated code in the init function. Is there a better way to do this in Swift?
I suspect the problem is that you need to explicitly conform the Apollo generated types to your protocol:
extension CurrentUser: UserProtocol { }
extension MyUser: UserProtocol { }
Remember that Swift is not duck-typed like some other languages, so a type with member var id: String is not UserProtocol until you declare it as such.
If for some reason you need to do some transformation of the Apollo types to fit the app models in the future, those extensions are a good place to do that, too.
Related
I am trying to create a protocol with default implementation that returns enum itself as string. But not able to find the correct syntax.
This is the code I tried so far, but it is not taking default implementation
protocol TestSelf {
static var desc: String { get set }
}
extension TestSelf {
get {
static var desc: String {
String(describing: self)
}
set {
print(\(new value))
}
}
enum Test: TestSelf { }
Access
print(Test.desc)
Asking me to implement the desc in the enum saying 'static var' declaration requires an initializer expression or an explicitly stated getter. I don't want to initialize it again. It should work with Default Implementation.
Ask:
At all places I don't need to write
String(describing: Test.self)
instead I can directly use
Test.desc
I think you want something like this (this is playground code):
protocol SelfDescriber {
static var descriptionOfSelf: String {get}
}
extension SelfDescriber {
static var descriptionOfSelf: String {
String(describing: Self.self)
}
}
enum Test: SelfDescriber {}
print(Test.descriptionOfSelf) // "Test"
I'm building a Converter to convert my DataObjects to ModelObjects and vice versa. I currently have two functions to do the converting. One for each conversion.
Currently, both of my conversion functions do exactly the same thing with exceptions to the type it takes and the type it returns. I was hoping I could write a generic function that would be able to handle both conversions because, otherwise, the code is exactly the same.
Here's what I've got: Obviously these are simplified examples
I've built a Protocol that contains the requirements for properties and an init(). I've implemented this Protocol and its init() in both the DataObject and ModelObject.
My Protocol:
protocol MyProtocol {
var id: UUID { get }
var name: String? { get }
init(id: UUID, name: String?)
}
My DataObject:
class DataObject: Object, MyProtocol {
#Persisted(primaryKey: true) var id: UUID
#Persisted var name: String?
required convenience init(id: UUID, name: String?) {
self.init()
self.id = id
self.name = name
}
}
My ModelObject:
struct ModelObject: MyProtocol {
var id: UUID
var name: String?
init(id: UUID, name: String?) {
self.id = id
self.name = name
}
}
Currently: This is an example what is currently doing the conversions. I have one like this for each conversion.
static func buildModelObject(object: DataObject) -> ModelObject {
let returnObject = ModelObject(id: object.id, name: object.name)
return returnObject
}
Desired Converter Function: I hope to accomplish something like this.
static func buildObject<O: MyProtocol, R: MyProtocol>(objectIn: O, returnType: R.Type) -> R {
let returnObject = returnType.init(id: objectIn.id, name: objectIn.name)
return returnObject
}
And I'm calling it like this:
let object = Converter.buildObject(objectIn: dataObject, returnType: ModelObject.self)
Obviously, this isn't working. Error: "Protocol 'MyProtocol' as a type cannot conform to the protocol itself". The error is on the function call. This is the only error XCode is showing me at compile.
I'm not certain what to do here or how to get it working. I'm not even confident that this error message is even helpful in any way.
The Question:
Is it even possible to accomplish something like this? If so, what am I missing? I'm still very unfamiliar with Swift Generics.
I don't have an issue with using multiple conversion functions as it's still better than getting the entire code base bogged down with Realm specific stuff. But, given that these functions are essentially the same, I'm hoping that Generics might be able to help reduce otherwise similar code into a single function.
Note: The DataObject is a Realm Object. I understand they have cool features like live/managed Objects. We're trying to keep our Persistence layer completely separated from the rest of the app with a single API/Entry Point. This is why I'm using these Converters.
You almost had it
func buildObject<R: MyProtocol>(objectIn: MyProtocol, returnType: R.Type) -> R {
let returnObject = returnType.init(id: objectIn.id, name: objectIn.name)
return returnObject
}
the key observation: at no point do we need the concrete type of objectIn, so just require the protocol type.
You don't need the other argument. The return type already provides the type information.
func buildObject<R: MyProtocol>(objectIn: some MyProtocol) -> R {
.init(id: objectIn.id, name: objectIn.name)
}
As suggested in the comments, this is more idiomatically expressed as an initializer.
extension MyProtocol {
init(_ objectIn: some MyProtocol) {
self.init(id: objectIn.id, name: objectIn.name)
}
}
I'm getting below JSON response from server, and displaying phone number on screen.
Now user can change/update any of phone number, so we have to update particular mobile number in same object and send it to server.
"phone_numbers": [
{
"type": "MOBILE",
"number": "8091212121"
},
{
"type": "HOME",
"number": "4161212943"
},
{
"type": "BUSINESS",
"number": "8091212344"
}
]
My model class is looks like this:
public struct Contact: Decodable {
public let phone_numbers: [Phone]?
}
public struct Phone: Decodable {
public let type: PhoneType?
public let number: String?
}
I'm struggling to update this JSON object for particular phone number.
For example, if I want to update BUSINESS number only in above array, What's best way to do it.
I'm using XCode 11 and Swift 5.
Because all your properties are defined as constants (let), nothing can be updated. You have to initialize and return a new Contact object with the updated phone numbers.
If you change the properties to var, then you can update:
public enum PhoneType: String, Decodable {
case mobile = "MOBILE"
case home = "HOME"
case business = "BUSINESS"
}
public struct Contact: Decodable {
public var phone_numbers: [Phone]?
mutating func update(phoneNumber: String, for type: PhoneType) {
guard let phone_numbers = self.phone_numbers else { return }
for (i, number) in phone_numbers.enumerated() {
if number.type == type {
self.phone_numbers![i].number = phoneNumber
}
}
}
}
public struct Phone: Decodable {
public var type: PhoneType?
public var number: String?
}
var contact = try! JSONDecoder().decode(Contact.self, from: jsonData)
contact.update(phoneNumber: "123456", for: .business)
I'm struggling to update this JSON object for particular phone number.
It shouldn't be a JSON object when you update it. Think of JSON as just a format for transferring data. Once transferred, you should parse it into something that you can work with, like an array of dictionaries or whatever. If you've done that, then more specific questions you might ask are:
How can I find a specific entry in an array?
How can I modify the fields of a struct?
How can I replace one entry in an array with another?
After looking at the definitions of your structures, I think the problem you're having probably has to do with how you've declared them:
public struct Phone: Decodable {
public let type: PhoneType?
public let number: String?
}
Because you used let to declare type and number, those fields cannot be changed after initialization. If you want the fields of a Phone struct to be modifiable, you need to declare them with var instead of let.
The same thing is true for your Contact struct:
public struct Contact: Decodable {
public let phone_numbers: [Phone]?
}
You've declared phone_numbers as an immutable array because you used let instead of var. If you want to be able to add, remove, or modify the array in phone_numbers, you need to use var instead.
The struct declarations you have right now work fine for reading the data from JSON because all the components of the JSON data are constructed using the values from the JSON. But again, you'll need to make those structs modifiable by switching to var declarations if you want to be able to make changes.
There are a couple of ways to approach this (I'm assuming PhoneType is an enum you have somewhere)
You can iterate over the array and guard for only business numbers, like so
for phone in phone_numbers{
guard phone.type == .MOBILE else { continue }
// Code that modifies phone
}
You can filter and iterate over the array, like so
phone_numbers.filter {$0.type == .BUSINESS }.forEach { phone in
// Modify phone here
}
You can then modify the right value in the array with it's index, like this
for (phoneIndex, phone) in phone_numbers.enumerated() {
guard phone.type == .BUSINESS else { continue }
phone_numbers[phoneIndex].type = ANOTHER_TYPE
}
Some can argue that the second is preferred over the first, because it is an higher order function, but in my day to day activities, I tend to use both and believe that this is a matter of taste
I'm trying to make a list with the raw values of the cases from an enumeration with the new SwiftUI framework. However, I'm having a trouble with conforming the 'Data' to Identifiable protocol and I really cannot find information how to do it. It tells me "Initializer 'init(_:rowContent:)' requires that 'Data' conform to 'Identifiable'" The stub provides me with an ObjectIdentifier variable in the last extension, but don't know what should I return. Could you tell me how do it? How do I conform Data to Identifiable, so I can make a list with the raw values?
enum Data: String {
case firstCase = "First string"
case secondCase = "Second string"
case thirdCase = "Third string"
}
extension Data: CaseIterable {
static let randomSet = [Data.firstCase, Data.secondCase]
}
extension Data: Identifiable {
var id: ObjectIdentifier {
return //what?
}
}
//-------------------------ContentView------------------------
import SwiftUI
struct Lala: View {
var name: String
var body: some View {
Text(name)
}
}
struct ContentView: View {
var body: some View {
return List(Data.allCases) { i in
Lala(name: i.rawValue)
}
}
}
⚠️ Try not to use already used names like Data for your internal module. I will use MyEnum instead in this answer
When something conforms to Identifiable, it must return something that can be identified by that. So you should return something unique to that case. For String base enum, rawValue is the best option you have:
extension MyEnum: Identifiable {
var id: RawValue { rawValue }
}
Also, enums can usually be identified by their selves:
extension MyEnum: Identifiable {
var id: Self { self }
}
⚠️ Note 1: If you return something that is unstable, like UUID() or an index, this means you get a new object each time you get the object and this will kill reusability and can cause epic memory and layout process usage beside view management issues like transition management and etc.
Take a look at this weird animation for adding a new pet:
Note 2: From Swift 5.1, single-line closures don't need the return keyword.
Note 3: Try not to use globally known names like Data for your own types. At least use namespace for that like MyCustomNameSpace.Data
Inline mode
You can make any collection iterable inline by one of it's element's keypath:
For example to self:
List(MyEnum.allCases, id:\.self)
or to any other compatible keypath:
List(MyEnum.allCases, id:\.rawValue)
✅ The checklist of the identifier: (from WWDC21)
Exercise caution with random identifiers.
Use stable identifiers.
Ensure the uniqueness, one identifier per item.
Another approach with associated values would be to do something like this, where all the associated values are identifiable.
enum DataEntryType: Identifiable {
var id: String {
switch self {
case .thing1ThatIsIdentifiable(let thing1):
return thing1.id
case .thing2ThatIsIdentifiable(let thing2):
return thing2.id
}
}
case thing1ThatIsIdentifiable(AnIdentifiableObject)
case thing2ThatIsIdentifiable(AnotherIdentifiableObject)
You can try this way:
enum MyEnum: Identifiable {
case valu1, valu2
var id: Int {
get {
hashValue
}
}
}
Copyright © 2021 Mark Moeykens. All rights reserved. | #BigMtnStudio
Combine Mastery in SwiftUI book
enum InvalidAgeError: String, Error , Identifiable {
var id: String { rawValue }
case lessThanZero = "Cannot be less than zero"
case moreThanOneHundred = "Cannot be more than 100"
}
I have a CoreDataStore class which has two generic placeholders and can be used for each entity type in the model. The idea is that it fetches an NSManagedObject subclass (based on one of the generic types) from the store, converts it into the appropriate object (based on the other generic type) and returns that object.
The purpose of this behaviour is so I'm keeping the Core Data aspects encapsulated and avoiding passing NSManagedObject instances all around the app.
Example potential usage
This is purely how the usage might look to further demonstrate what I am trying to achieve.
let personStore = CoreDataStore<ManagedPerson, Person>()
let personData = personStore.fetchSomeObject() // personData is a value type Person
I have the following code, separated over several files but shown here in a modified fashion for simplicity.
import Foundation
import CoreData
// MARK: - Core Data protocol and managed object
protocol ManagedObjectProtocol { }
class ManagedPerson: NSManagedObject, ManagedObjectProtocol {
var title: String?
}
class ManagedDepartment: NSManagedObject, ManagedObjectProtocol {
var name: String?
}
// MARK: - Simple struct representations
protocol DataProtocol {
typealias ManagedObjectType: ManagedObjectProtocol
init(managedObject: ManagedObjectType)
}
struct Person {
var title: String?
}
struct Department {
var name: String?
}
extension Person: DataProtocol {
typealias ManagedObjectType = ManagedPerson
init(managedObject: ManagedPerson) {
self.title = managedObject.title
}
}
extension Department: DataProtocol {
typealias ManagedObjectType = ManagedDepartment
init(managedObject: ManagedDepartment) {
self.name = managedObject.name
}
}
class CoreDataStore<ManagedObject: ManagedObjectProtocol, DataObject: DataProtocol> {
func fetchSomeObject() -> DataObject {
var managedObject: ManagedObject // fetch an NSManagedObject
// Error here
return DataObject(managedObject: managedObject)
}
}
The error I am receiving is when I try to initialise the struct in fetchSomeObject:
Cannot invoke initializer for type 'DataObject' with an argument list of type '(managedObject: ManagedObject)'
Obviously the compiler can't figure out that the DataObject (which is restricted to types conforming to DataProtocol) can be initialised with a ManagedObject (which is restricted to types conforming to ManagedObjectProtocol) despite it being declared as such in DataProtocol.
Is there any way to achieve this functionality? Additionally is this a reasonable approach or am I completely off the wall with this?
Update
After a bit of digging it seems that Swift generics are invariant which I believe is causing what I'm running into.
Think your CoreDataStore again, for example, CoreDataStore<ManagedPerson, Department> doesn't make any sense. Why not? Because the Department is a DataProtocol without problem, but its corresponding typealias ManagedObjectType is not ManagedPerson.
The reason why your code won't compile is just the same. Here return DataObject(managedObject: managedObject) you can't initialize an DataObject from an armbitary ManagedObject, only a DataObject.ManagedObjectType is acceptable.
So what you need is a type constraint, add this where clause, your code should work:
class CoreDataStore<ManagedObject: ManagedObjectProtocol, DataObject: DataProtocol
where DataObject.ManagedObjectType == ManagedObject>