Type-Safe User Defaults

TSUD (pronounced "tsud") stands for Type-Safe User Defaults and is an experimental Swifty wrapper around NSUserDefaults.

License

Public domain. Do what you feel like. Credit is appreciated but not required.

Example Use

To declare a key, write a struct conforming to the TSUD protocol. Inside, implement a single static property called defaultValue which contains the value to be returned if UserDefaults doesn't contain a value:

struct fontSize: TSUD {
    static let defaultValue = 12.0
}

To read or write the value, use the value property on the struct:

let font = NSFont.systemFont(ofSize: fontSize.value)
fontSize.value = 14.0

Since value is just a property, you can do disturbing and unnatural things like += to it.

fontSize.value += 5.0

If you want to be able to detect the lack of a value and handle it specially rather than getting a default value, declare defaultValue to be optional and set it to nil:

struct username: TSUD {
    static let defaultValue: String? = nil
}

Then use it like any other optional:

if let username = username.value {
    field.string = username
} else {
    username.value = promptForUsername()
}

By default, TSUD types correspond to a UserDefaults key matching their type name. These examples would be stored under "fontSize" and "username". If you need to override this (for example, because you want to access a key that has a space in it, or you don't like the key's capitalization in your code), implement the stringKey property:

struct hasWidgets: TSUD {
    static let defaultValue = false
    static let stringKey = "Has Widgets"
}

Arbitrary Codable types are supported. They are encoded as property list objects:

struct Person: Codable {
    var name: String
    var quest: String
    var age: Int
}

struct testPerson: TSUD {
    static let defaultValue: Person? = nil
}

If you prefer, you can also use methods to get and set the value:

if hasWidgets.get() {
    hasWidgets.set(false)
}

These methods allow you to specify the UserDefaults object to work with, in the unlikely event that you want to work with something other than UserDefaults.standard:

let otherDefaults = UserDefaults(suitName: "...")!
if hasWidgets.get(otherDefaults) {
    // That other thing has widgets!
}

If you want to access the value in another UserDefaults instance as a mutable value, there's a subscript which takes a UserDefaults instance and provides the value. Unfortunately, Swift doesn't allow static subscripts, so you have to instantiate the key type:

fontSize()[otherDefaults] += 10.0