/// <summary>
/// Remove a cache entry from the <see cref="IMemoryCache"/> with the key
/// generated by the key factory function.
/// </summary>
/// <typeparam name="TSource">The type of the value.</typeparam>
/// <param name="observable">The parent observable.</param>
/// <param name="keyFactory">The key factory function.</param>
/// <returns>An instance of <see cref="IProviderObservable{TSource}"/>.</returns>
public static IProviderObservable <TSource> RemoveMemoryCacheEntry <TSource>(
this IProviderObservable <TSource> observable, Func <TSource, object> keyFactory) =>
observable.Do(s =>
{
var memoryCache = observable.ServiceProvider.GetService <IMemoryCache>();
var key = keyFactory(s);
memoryCache.Remove(key);
});
