State swapping

Swapper.cs

using System;
using System.Reactive.Disposables;

static partial class Swapper
{
    public static Func<T, T> Create<T>(Func<T> getter, Action<T> setter)
    {
        if (getter == null) throw new ArgumentNullException("getter");
        if (setter == null) throw new ArgumentNullException("setter");

        return v =>
        {
            var swapped = getter();
            setter(v);
            return swapped;
        };
    }

    public static IDisposable Scope<T>(this Func<T, T> swapper, T value)
    {
        var swapped = swapper(value);
        return Disposable.Create(() => swapper(swapped));
    }
}