C# 7.0 Generalized async return types - Minimum Implementation Code for LinqPad 5

GeneralizedAsyncReturnTypes-MinImpl.linq

<Query Kind="Program">
  <Namespace>System.Runtime.CompilerServices</Namespace>
  <Namespace>System.Threading.Tasks</Namespace>
</Query>

static void Main() {
    var result = GetValueAsync().Result;
    Console.WriteLine(result);
}

public static async MyTask<int> GetValueAsync() {
    await Task.Delay(1000);
    return 123;
}

[AsyncMethodBuilder(typeof(MyTaskMethodBuilder<>))]
public struct MyTask<T> {
    private Task<T> _task;

    public MyTask(Task<T> task) => _task = task;

    public T Result => _task.Result;
}

public struct MyTaskMethodBuilder<T> {
    private AsyncTaskMethodBuilder<T> _methodBuilder;

    public static MyTaskMethodBuilder<T> Create() =>
        new MyTaskMethodBuilder<T> { _methodBuilder = AsyncTaskMethodBuilder<T>.Create() };

    public void Start<TStateMachine>(ref TStateMachine stateMachine)
        where TStateMachine : IAsyncStateMachine {
        _methodBuilder.Start(ref stateMachine);
    }

    public void SetStateMachine(IAsyncStateMachine stateMachine) {
        _methodBuilder.SetStateMachine(stateMachine);
    }

    public void SetException(Exception exception) {
        _methodBuilder.SetException(exception);
    }

    public void SetResult(T result) {
        _methodBuilder.SetResult(result);
    }

    public void AwaitOnCompleted<TAwaiter, TStateMachine>(
        ref TAwaiter awaiter, ref TStateMachine stateMachine)
        where TAwaiter : INotifyCompletion
        where TStateMachine : IAsyncStateMachine {
        _methodBuilder.AwaitOnCompleted(ref awaiter, ref stateMachine);
    }
    public void AwaitUnsafeOnCompleted<TAwaiter, TStateMachine>(
        ref TAwaiter awaiter, ref TStateMachine stateMachine)
        where TAwaiter : ICriticalNotifyCompletion
        where TStateMachine : IAsyncStateMachine {
        _methodBuilder.AwaitUnsafeOnCompleted(ref awaiter, ref stateMachine);
    }

    public MyTask<T> Task => new MyTask<T>(_methodBuilder.Task);
}


}
namespace System.Runtime.CompilerServices {
    public sealed class AsyncMethodBuilderAttribute : Attribute {
        public AsyncMethodBuilderAttribute(Type builderType) {
            BuilderType = builderType;
        }
        
        public Type BuilderType { get; }
    }
}
class EOF {