Atomic

// https://www.vadimbulavin.com/swift-atomic-properties-with-property-wrappers/

/*
Although get and set are individually atomic, the combination of both is not. 
Incrementing x is not atomic, since it first calls get and then set:
*/
@propertyWrapper
struct Atomic<Value> {
    private let queue = DispatchQueue(label: "com.vadimbulavin.atomic")
    private var value: Value

    init(wrappedValue: Value) {
        self.value = wrappedValue
    }
    
    var wrappedValue: Value {
        get {
            return queue.sync { value }
        }
        set {
            queue.sync { value = newValue }
        }
    }
    
    func mutate(_ mutation: (inout Value) -> Void) {
        queue.sync { mutation(&value) }
    }
}

struct MyStruct {
    @Atomic var x = 0
}

// Verison 2
/* 
When we update a value in a collection (Array, Set and Dictionary), 
both get and set are called. Make sure to use the mutate() method in such cases:
*/
@propertyWrapper
class Atomic<T> {
    private let queue = DispatchQueue(label: "com.vadimbulavin.atomic")
    var projectedValue: Atomic<T> { return self }
    var value: T

    init(wrappedValue: T) {
        self.value = wrappedValue
    }
    
    var wrappedValue: T {
        get {
            print("wrappedValue get \(value)")
            return queue.sync { value }
        }
        set {
            print("wrappedValue set \(newValue) -> \(value)")
            queue.sync { value = newValue }
        }
    }
    
    func mutate(_ mutation: (inout T) -> Void) {
       queue.sync { mutation(&value) }
   }
    func help() {
        print("help")
    }
}