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A Swift extension to use string-based API in a type-safe way.
.package(url: "https://github.com/ddddxxx/GenericID.git", from: "v0.7.0")

This project is currently in beta and APIs are subject to change.


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A Swift extension to use string-based API in a type-safe way.

All these fantastic API are compatible with traditional string-based API.


  • Swift 5.2 (Xcode 11.4)

Type-safe UserDefaults

You can use NSUbiquitousKeyValueStore with almost the same API.

1. Define your keys

extension UserDefaults.DefaultKeys {
    static let intKey   = Key<Int>("intKey")
    static let colorKey = Key<Color>("colorKey", transformer: .keyedArchive)
    static let pointKey = Key<CGPoint>("pointKey", transformer: .json)

2. Have fun!

let ud = UserDefaults.standard

// Get & Set
let value = ud[.intKey]
ud[.stringKey] = "foo"

// Modify
ud[.intKey] += 1
ud[.stringKey] += "bar"

// Typed array
ud[.intArrayKey][0] += 1

// Work with NSKeyedArchiver
ud[.colorKey] = UIColor.orange

// Work with JSONEncoder
ud[.pointKey] = CGPoint(x: 1, y: 1)
ud[.pointKey]?.x += 1

// Modern Key-Value Observing
let observation = defaults.observe(.someKey, options: [.old, .new]) { (defaults, change) in

// KVO with deserializer
let observation = defaults.observe(.rectKey, options: [.old, .new]) { (defaults, change) in
    // deserialized automatically
    if let rect = change.newValue {
        someView.frame = rect

// Register with serializer
ud.register(defaults: [
    .intKey: 42,
    .stringKey: "foo",
    .colorKey: UIColor.blue, // serialized automatically
    .pointKey: CGPoint(x: 1, y: 1),

Default value

If associated type of a key conforms DefaultConstructible, a default value will be constructed for nil result.

public protocol DefaultConstructible {

Here's types that conforms DefaultConstructible and its default value:

Type Default value
Bool false
Int 0
Float/Double 0.0
String ""
Data [empty data]
Array []
Dictionary [:]
Optional nil

Note: Optional also conforms DefaultConstructible, therefore a key typed as DefaultKey<Any?> aka DefaultKey<Optional<Any>> will still returns nil, which is the result of default construction of Optional.

You can always associate an optional type if you want an optional value.

Type-safe UITableViewCell / UICollectionViewCell

1. Define your reuse identifiers

extension UITableView.CellReuseIdentifiers {
    static let customCell : ID<MyCustomCell> = "CustomCellReuseIdentifier"

2. Register your cells

tableView.register(id: .customCell)

3. Dequeue your cells

let cell = tableView.dequeueReusableCell(withIdentifier: .customCell, for: indexPath)
// Typed as MyCustomCell

XIB-based cells

// That's it!
extension MyCustomCell: UINibFromTypeGettable

// Or, incase your nib name is not the same as class name
extension MyCustomCell: UINibGettable {
    static var nibName = "MyNibName"

// Then register
tableView.registerNib(id: .customCell)

Type-safe Storyboard

1. Define your storyboards identifiers

extension UIStoryboard.Identifiers {
    static let customVC: ID<MyCustomViewController> = "CustomVCStoryboardIdentifier"

2. Use It!

// Also extend to get main storyboard
let sb = UIStoryboard.main()

let vc = sb.instantiateViewController(withIdentifier: .customVC)
// Typed as MyCustomViewController

Type-safe Associated Object

// Define your associate keys
extension YourClass.AssociateKeys {
    static let someKey: Key<Int> = "someKey"

// Use it!
yourObject[.someKey] = 42


GenericID is available under the MIT license. See the LICENSE file.


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Last commit: 3 weeks ago

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iOS Software Engineer @ Perry Street Software
Perry Street Software is Jack’d and SCRUFF. We are two of the world’s largest gay, bi, trans and queer social dating apps on iOS and Android. Our brands reach more than 20 million members worldwide so members can connect, meet and express themselves on a platform that prioritizes privacy and security. We invest heavily into SwiftUI and using Swift Packages to modularize the codebase.

Swiftpack is being maintained by Petr Pavlik | @ptrpavlik | @swiftpackco | API