c# PassThroughFlow example Akka.Streams

gistfile1.cs

/// <summary>
    /// As translated from: https://doc.akka.io/docs/alpakka/current/patterns.html#passthrough
    /// </summary>
public class PassThroughFlow
    {
        public static IGraph<FlowShape<A, (T,A)>, NotUsed> create<A,T>(Flow<A, T, NotUsed> flow) {
            return create(flow, Keep.Both);
        }
        
        /// <summary>
        ///                     a=>transform=>a1
        ///                    /                 \
        ///                   /                   \
        /// a=>(a, a)=>unzip -                     zip=>(a1, a)=> a
        ///                   \                   /
        ///                    \                 /
        ///                     --------a-------- 
        /// </summary>
        /// <param name="flow"></param>
        /// <param name="output"></param>
        /// <typeparam name="A"></typeparam>
        /// <typeparam name="T"></typeparam>
        /// <typeparam name="O"></typeparam>
        /// <returns></returns>
        private static  IGraph<FlowShape<A, O>, NotUsed> create<A, T, O>(
            Flow<A, T, NotUsed> flow, Func<T, A, O> output) {
            return Flow.FromGraph(
                GraphDsl.Create(builder => {
                    UniformFanOutShape<A, A> broadcast = builder.Add(new Broadcast<A>(2));
                    FanInShape<T, A, O> zip = builder.Add(new ZipWith<T,A, O>(output));
                    builder.From(broadcast.Out(0)).Via(builder.Add(flow)).To(zip.In0);
                    builder.From(broadcast.Out(1)).To(zip.In1);
                    return new FlowShape<A,O>(broadcast.In, zip.Out);
            }));
        }
        
         public static async Task Example()
        {
            using var system = ActorSystem.Create("passtroughflow");
            using var materialiser = system.Materializer();
            {
                Source<int,NotUsed> source = Source.From(new []{1,2,3});
                // Pass through this flow maintaining the original message
                Flow<int, int, NotUsed> passThroughMe = Flow.Create<int>().Select(i => i * 10);
                        
                IImmutableList<(int, int)> ret = await source.Via(PassThroughFlow.create(passThroughMe)).RunWith(Sink.Seq<(int,int)>(),materialiser);
                        
                IImmutableList<(int, int)> list = ret;
                list[0].Equals((10,1));
                list[0].Equals((20,2));
                list[0].Equals((30,3));
            }
        }
    }