Swift @NSCopying

NSCopying_test.swift

import UIKit

/*
    I'm not sure why `@NSCopying` doesn't seem to be copying the object in the example below.
    I'm attempting to write code that follows the "initialization with a configuration object" pattern, like `NSURLSession`.
    Ideally the configuration would be a struct, but since I'm still interoperating with Obj-C that's not an option.
*/

class Foo : NSObject, NSCopying {
    var bar = "bar"
    var baz = 1
    func copyWithZone(zone: NSZone) -> AnyObject {
        let copy = Foo()
        copy.bar = bar
        copy.baz = baz
        return copy
    }
}

class Test : NSObject {
    @NSCopying private(set) var foo : Foo
    init(foo : Foo) {
        self.foo = foo
        super.init()
    }
}

var initialFoo = Foo()
initialFoo.bar = "initial"
initialFoo.baz = 0

let test = Test(foo: initialFoo) // `test`'s version of `foo` should be a copy of `initialFoo`

test.foo.bar // "initial"
test.foo.baz // 0

var readFoo = test.foo // `readFoo` should be a copy of `test`'s copy of `initialFoo`

initialFoo === readFoo // true

readFoo.bar = "changed"
readFoo.baz = 100

test.foo.bar // "changed"
test.foo.baz // 100

Values set during initialization are not cloned. You have to make var foo an optional and assign initialFoo to it in order to get a copy.