Un-Winding a C# Async/Await

AwaiterFoo.cs

//////////////////////////////////////////////////////////////////////////////////////
// https://bytelanguage.net/2020/05/31/tpl-and-asynchronous-programming/
// https://www.markopapic.com/csharp-under-the-hood-async-await/
using System;
using System.Threading.Tasks;

namespace MyApplication{public class Program{
   public static void Main(string[] args){
      Foo(10).Wait();
   }

   static async Task Foo(int delay){
      Console.WriteLine("FooStart");
      await Task.Delay(delay);
      Console.WriteLine(delay);
      await Bar();
      Console.WriteLine("FooDone");
   }

   static async Task Bar(){
      await Task.Delay(100);
   }
}}

UnWoundFoo.cs

//////////////////////////////////////////////////////////////////////////////////////
// https://bytelanguage.net/2020/06/08/asynchronous-code-behind-the-scenes-004/
using System;
using System.Threading.Tasks;
using System.Runtime.CompilerServices;

namespace MyApplication{public class Program{
   struct FooStateMachine : IAsyncStateMachine{
      public int delay;
      
      public Task Task{
         get => t__builder.Task;
      }

      public void Start(){
         i__state   = -1;
         t__builder = AsyncTaskMethodBuilder.Create();
         t__builder.Start(ref this);
      }

      AsyncTaskMethodBuilder t__builder;
      int i__state;
      TaskAwaiter awaiter;
      
      void IAsyncStateMachine.MoveNext(){
         try{
            switch(i__state){
             case -2: goto Completed;
             case -1: goto Started;
             case  0: goto ResumePoint1; // Task.Delay(delay); has completed
             case  1: goto ResumePoint2; // Bar(); has completed
             default: goto Completed;
            }
            Started:
               Console.WriteLine("FooStart");
               awaiter = Task.Delay(delay).GetAwaiter();
      
               i__state = 0;
               if(!awaiter.IsCompleted){
                  t__builder.AwaitUnsafeOnCompleted(ref awaiter, ref this);
                  return;
               }

            ResumePoint1:
               awaiter.GetResult();
      
               Console.WriteLine(delay);
               awaiter = Bar().GetAwaiter();
      
               i__state = 1;
               if(!awaiter.IsCompleted){
                  t__builder.AwaitUnsafeOnCompleted(ref awaiter, ref this);
                  return;
               }

            ResumePoint2:
               awaiter.GetResult();
      
               Console.WriteLine("FooDone");
      
               awaiter = default(TaskAwaiter);

            Completed:
               i__state = -2;
         }catch (Exception exception){
            i__state = -2;
            t__builder.SetException(exception);
            return;
         }
         t__builder.SetResult();
      }

      void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine stateMachine){
         t__builder.SetStateMachine(stateMachine);
      }
   } 

   public static void Main(string[] args){
      Foo(10).Wait();
   }

   static Task Foo(int delay){
      var FooMachine   = new FooStateMachine();
      FooMachine.delay = delay;
      FooMachine.Start();
      return FooMachine.Task;
   }

   static async Task Bar(){
      await Task.Delay(100);
   }
}}