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Small collection of property wrappers.
.package(url: "https://github.com/mediamonks/MMMPropertyWrappers.git", from: "0.1.0")


Build Test

Small collection of property wrappers.

(This is a part of MMMTemple suite of iOS libraries we use at MediaMonks.)



source 'https://github.com/mediamonks/MMMSpecs.git'
source 'https://github.com/CocoaPods/Specs.git'
pod 'MMMPropertyWrappers'


.package(url: "https://github.com/mediamonks/MMMPropertyWrappers", .upToNextMajor(from: "0.1.0"))


Simple examples for each property wrapper.


A wrapper that allows to set a value only once after setting the initial value. This comes in useful in instances where you want to freeze the value after configuring it.

For instance on configuration object, where you want to assign a default value, but give the user the ability to alter this value in a configuration callback.

class Config {
    @Once var myValue: Bool = false
    @Once var otherValue: Bool = false

    init(_ config: (Config) -> Void) {

// At call site
let config = Config {
    $0.myValue = true

Now config.myValue is 'frozen', if you try setting it afterwards it will throw an assertionFailure. However, config.otherValue is still open, since the user decided not to alter that value, so it's wise to call .freeze() after your configuration block.

init(_ config: (Config) -> Void) {



A wrapper that will trigger a SimpleEvent or LazySimpleEvent, e.g. AnySimpleEvent when the value changes. The value should conform to Equatable, and the enclosing class to EventTriggerable.

This removes a lot of boilerplate code, going from:

protocol ViewModel {

	var foo: String { get }
	var bar: String { get }

	var didChange: SimpleEventObservable { get }

class DefaultViewModel: ViewModel {

	public private(set) var foo: String {
		didSet {
			_didChange.trigger(if: foo != oldValue)

	public private(set) var bar: String {
		didSet {
			_didChange.trigger(if: bar != oldValue)

	private let _didChange = SimpleEvent()
	public var didChange: SimpleEventObservable { _didChange }


class DefaultViewModel: ViewModel, EventTriggerable {

	@EventTrigger public private(set) var foo: String
	@EventTrigger public private(set) var bar: String

	private let _didChange = SimpleEvent()
	public var didChange: SimpleEventObservable { _didChange }

Every time foo or bar is set, and the value != oldValue, the _didChange event will trigger.

If your property does not conform to Equatable, you could use @LenientEventTrigger.


Same as @EventTrigger, but without requiring to conform to Equatable, this will trigger every time the value hits didSet.


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