/// <summary>
/// Remove a cache entry from the <see cref="IDistributedCache"/> 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> RemoveDistributedCacheEntry <TSource>(
this IProviderObservable <TSource> observable, Func <TSource, string> keyFactory) =>
observable.DoAsync(async s =>
{
var distributedCache = observable.ServiceProvider.GetService <IDistributedCache>();
var key = keyFactory(s);
await distributedCache.RemoveAsync(key);
});
