public class Program
{
  static async Task Main()
  {
    var result = (int)await ReturnCallAsync<Func<string, Task<int>>>(Foo, new object[]{"0123456789"});
    Console.WriteLine(result);
    await CallAsync<Func<IEnumerable<string>, Task>>(Bar, new object[]{new[] {"foo", "bar", "zot"}});
  }

  static async Task<object> ReturnCallAsync<T>(T func, object[] values) where T : MulticastDelegate
  {
    var returnType = func.Method.ReturnType;
    if (!(typeof(Task).IsAssignableFrom(returnType) && returnType.IsGenericType))
      throw new InvalidOperationException();
    dynamic awaiter = func.Method.Invoke(func.Target, values);
    await awaiter;
    return awaiter.GetAwaiter().GetResult();
  }

  static async Task CallAsync<T>(T action, object[] values) where T : MulticastDelegate
  {
    var returnType = action.Method.ReturnType;
    if (!(typeof(Task).IsAssignableFrom(returnType) && !returnType.IsGenericType))
      throw new InvalidOperationException();
    dynamic awaiter = action.Method.Invoke(action.Target, values);
    await awaiter;
  }

  static async Task<int> Foo(string argument)
  {
    await Task.Yield();
    return argument?.Length ?? -1;
  }

  static async Task Bar(IEnumerable<string> arguments)
  {
    await Task.Yield();
    Console.WriteLine(arguments?.Any() ?? false ? arguments.Aggregate((a,b)=>$"{a},{b}") : "sequence is empty");
  }
}