Atomic.swift

protocol Lock {
    func lock() throws
    func unlock()
}

protocol Atomic {
    associatedtype Protected
    associatedtype Primitive: Lock
    
    var lock: Primitive { get }
    
    var value: Protected { get set }
}

extension Atomic {
    var value: Protected {
        get {
            try! lock.lock()
            defer { lock.unlock() }
            return value
        }
        set {
            try! lock.lock()
            defer { lock.unlock() }
            value = newValue
        }
    }
}


class SpinLock: Lock {
    func lock() throws { }
    func unlock() { }
}

class AtomicSpinLock<P>: Atomic {
    typealias Protected = P
    var lock: SpinLock
}

var i: AtomicSpinLock<Int>