A protocol-centric, type and queue safe key-value workflow.

.Package(url: "https://github.com/metasmile/PropertyKit.git")

extension Defaults: PropertyDefaults {
    public var autoStringProperty: String? {
        set{ set(newValue) } get{ return get() }
    }
    public var autoDateProperty: Date? {
        set{ set(newValue) } get{ return get() }
    }
}

var sharedDefaults = Defaults()
sharedDefaults.autoStringProperty = "the new value will persist in shared scope"
// sharedDefaults.autoStringProperty == Defaults.shared.autoStringProperty

Defaults.shared.autoStringProperty = "another new value will persist in shared scope"
// Defaults.shared.autoStringProperty == sharedDefaults.autoStringProperty

var localDefaults = Defaults(suiteName:"local")
localDefaults.autoStringProperty = "the new value will persist in local scope"
// localDefaults.autoStringProperty != Defaults.shared.autoStringProperty

public struct CustomValueType: Codable{
    var key:String = "value"
    var date:Date?
    var data:Data?
}
extension Defaults: PropertyDefaults {
    // non-optional - must define the default value with the keyword 'or'
    public var autoCustomNonOptionalProperty: CustomValueType {
        set{ set(newValue) } get{ return get(or: CustomValueType()) }
    }
    // optional with/without setter default value
    public var autoCustomOptionalProperty: CustomValueType? {
        set{ set(newValue) } get{ return get() }
    }
    public var autoCustomOptionalPropertySetterDefaultValue: CustomValueType? {
        set{ set(newValue, or: CustomValueType()) } get{ return get() }
    }
}

//CodeFile1_ofLargeProject.swift
protocol MyDefaultsKeysUsingInA : PropertyDefaults{
    var noThisIsMyKeyNotYours:Int?{ get }
}
extension Defaults : MyDefaultsKeysUsingInA{
    var noThisIsMyKeyNotYours:Int?{ set{ set(newValue) } get{ return get() } }
}

//CodeFile2_ofLargeProject.swift
protocol MyDefaultsKeysUsingInB : PropertyDefaults{
    var noThisIsMyKeyNotYours:Int?{ get }
}
extension Defaults : MyDefaultsKeysUsingInB{
    var noThisIsMyKeyNotYours:Int?{ set{ set(newValue) } get{ return get() } }
}

// MyFile.swift
fileprivate protocol PrivateDefaultKeysInThisSwiftFile: PropertyDefaults{
    var filePrivateValue: String? {set get}
}

extension Defaults: PrivateDefaultKeysInThisSwiftFile {
    public var filePrivateValue: String? {
        set{ set(newValue) } get{ return get() }
    }
}

// Can access - 👌
Defaults.shared.filePrivateValue

// MyOtherFile.swift

// Not able to access - ❌
Defaults.shared.filePrivateValue

var p1:Int{
    Defaults.shared.set(2)  
    return Defaults.shared.get(or:0)  
}
var p2: Int{
    return Defaults.shared.get(or:0)  
}

p1 // == 2
p2 // == 0
//It means that are function/property-scoped capsulated defaults values.

class WatchableObject:NSObject, PropertyWatchable{
    @objc dynamic
    var testingProperty:String?
}

let object = WatchableObject()
object.watch(\.testingProperty) {
    object.testingProperty == "some value"
    //Do Something.
}

object.testingProperty = "some value"

// Default option is the default of NSKeyValueObservation (.new)
// (WatchableObject, NSKeyValueObservedChange<Value>)
object.watch(\.testingProperty, options: [.initial, .new, .old]) { (target, changes) in     
    target.testingProperty == "some value"
    //Dd Something.
}

let object = WatchableObject()
object.testingProperty = "initial value"
config.watch(\.testingProperty, options: [.initial]) { (o, _) in
    o.testingProperty == "initial value"
}

object.watch(\.testingProperty) {
    // Listening as a unique observer 1
}

object.watch(\.testingProperty) {
    // Listening as a unique observer 2
}

object.watch(\.testingProperty, id:"myid", options:[.old]) {
    // Listening as an observer which has identifier "myid"
}

// total 3 separated each observers are listening each callbacks.

// Remove only an observer which has "myid" only
object.unwatch(\.testingProperty, forIds:["myid"])

// Remove all observers that are watching ".testingProperty"
object.unwatch(\.testingProperty)

//Automatically remove all observers in current file.
object.unwatchAllFilePrivate()

//Automatically remove entire observers in application-wide.
object.unwatchAll()