Bolero (and Blazor and Elmish) and Rx.NET lazy component

ReactiveLazyComponent.fs

open Bolero
open Elmish
open System.Reactive.Disposables
open System.Reactive.Subjects

type ReactiveLazyComponent<'model, 'event, 'msg>() =
  inherit Bolero.ElmishComponent<'model, 'msg>()
  let subject    = new Subject<'event>()
  let observer   = subject :> IObserver<_>
  let observable = subject :> IObservable<_>
  let mutable subscription = Disposable.Empty

  [<Parameter>]
  member val ViewFunction =
    Unchecked.defaultof<'model -> Dispatch<'event> -> Node> with get, set

  [<Parameter>]
  member val StreamFunction : IObservable<'event> -> IObservable<'msg> =
    Unchecked.defaultof<IObservable<'event> -> IObservable<'msg>> with get, set

  override this.View model dispatch =
    do if obj.ReferenceEquals(subscription, Disposable.Empty)
       then subscription <- this.StreamFunction observable |> Observable.subscribe dispatch
    this.ViewFunction model observer.OnNext

  interface System.IDisposable with
    member _.Dispose() =
      subject.Dispose()
      subscription.Dispose()