Open Radar

 
Summary: It seems that playgrounds hold on to weak instances unnecessarily. Attached is a sample playground to demonstrate what I'm talking about.

If you copy the `Weak` enum definition and do this in a sample project, it deallocates properly.

Contents of the playground:

```
import Foundation

enum Weak<T> {
    class Box {
        weak var object: AnyObject?
        init(_ object: AnyObject) { self.object = object }
    }

    case reference(Box)
    case value(T)

    init(_ instance: T) {
        if type(of: instance) is AnyClass {
            self = .reference(Box(instance as AnyObject))
        } else {
            self = .value(instance)
        }
    }

    var instance: T? {
        switch self {
        case .reference(let box):
            return box.object as? T
        case .value(let instance):
            return instance
        }
    }
}

class A {}
let two = Weak(A())
two.instance   // should be `nil`, but is `A`
```