===========
Disposables
===========

Asynchronous disposables are similar to `IDisposable
<https://docs.microsoft.com/en-us/dotnet/api/system.idisposable?view=netcore-2.1>`_
but with the difference that it encapsulates an async dispose method
called `DisposeAsync`.

.. code:: fsharp

    type AsyncDisposable (cancel) =
        interface IAsyncDisposable with
            member this.DisposeAsync () =
                async {
                    do! cancel ()
                }

In additon the following static members have been defined:

- **Create** : ``(unit -> Async<unit>) -> IAsyncDisposable``, creates an
  ``IAsyncDisposable`` from an async cancel function. Same instantiating
  the object, but the return value here is anonymous.

- **Empty** : ``unit -> IAsyncDisposable``, creates an empty disposable
  that will do nothing if it's disposed.

- **Composite** : ``seq<IAsyncDisposable> -> IAsyncDisposable``, creates a
  disposable from a sequence of disposables. If disposed then all the
  contained disposables will also be disposed.

The ``SubscribeAsync`` method for async observables returns an async
disposable, and to cancel the subscription you need to call the
`DisposeAsync` method.

.. code:: fsharp

    let xs = ofSeq <| seq { 1 .. 5 }
    let obv = MyObserver<int>()
    let! subscription = xs.SubscribeAsync obv

    // Unsubscribe
    do! subscription.DisposeAsync ()