Return new task with return value, using the Task constructor with async action

Question

Maybe someone can explain, why this is working:

var task = new Task(async () =>
{
    var noSolution = await AsyncMethodWithBoolReturnValue();

    if (noSolution)
    {
        await DoSomethingAsync();
    }
});

But using the generic to specify the return value is not possible?

var task = new Task<bool>(async () =>
{
    var noSolution = await AsyncMethodWithBoolReturnValue();

    if (noSolution)
    {
        await DoSomethingAsync();
    }

    return noSolution;
});

Thanks a lot!

Answer 1

The non-generic Task constructor is not async-friendy. The async delegate is async void. What you really want is probably a nested Task<Task>. This is a Task that represents the creation of another Task. When the outer Task completes, it means that the inner Task has been created:

Task<Task> taskTask = new(async () =>
{
    bool noSolution = await AsyncMethodWithBoolReturnValue();

    if (noSolution)
    {
        await DoSomethingAsync();
    }
});

Or with result:

Task<Task<bool>> taskTask = new(async () =>
{
    bool noSolution = await AsyncMethodWithBoolReturnValue();

    if (noSolution)
    {
        await DoSomethingAsync();
    }

    return noSolution;
});

You can then use the Unwrap method, to create a new proxy Task that represents the completion of both the outer and inner tasks. I don't know what exactly you want to do, but most likely you will need this.

Also make sure that when you Start/RunSynchronously the taskTask, you specify explicitly the TaskScheduler, so that your code complies with the CA2008 guideline:

taskTask.RunSynchronously(TaskScheduler.Default);