 }
 
 // Concrete future wrapper that will never get filled.
-private final class UnfilledFuture<Value>: FutureBase<Value> {
+private final class Never<Value>: FutureBox<Value> {
     override init() {}
 
     override func upon(queue: dispatch_queue_t, body: Value -> ()) {}

*/

// Abstract class that fake-conforms to `FutureType` for use by `Future`.
private class FutureBase<Value>: FutureType {
    func upon(queue: dispatch_queue_t, body: Value -> ()) {
        fatalError()
    }

}

// Concrete future wrapper for an always-filled future.
private final class Always<Value>: FutureBox<Value> {
    let value: Value
    init(value: Value) {
        self.value = value
