 
 /// A disposable that only flips `disposed` upon disposal, and performs no other
 /// work.
-class SimpleDisposable: Disposable {
+@final class SimpleDisposable: Disposable {
 	var _disposed = Atomic(false)
 
 	var disposed: Bool {


/// A disposable that, upon deinitialization, will automatically dispose of
/// another disposable.
class ScopedDisposable: Disposable {
	/// The disposable which will be disposed when the ScopedDisposable
	/// deinitializes.
	let innerDisposable: Disposable

}

/// A disposable that will optionally dispose of another disposable.
@final class SerialDisposable: Disposable {
	struct _State {
		var innerDisposable: Disposable? = nil
		var disposed = false
