Preserve exception when continuing Task<T>

Question

I've got a Task<T>:

Task<A> someTask = ...

This task can result in being successful, faulted or cancelled.

I want to transform the result when the task is successful, and preserve the outcome if not.

This seems to be really difficult when someTask throws an exception.

What I've tried:

Task<B> resultTask = StartMyTask().ContinueWith<B>(
    t => Foo(t.Result),
    TaskContinuationOptions.OnlyOnRanToCompletion);

This results in resultTask being cancelled if someTask faults. I want it to fault.

Task<B> resultTask = StartMyTask().ContinueWith<B>(
    t => Foo(t.Result));

This breaks into the Visual Studio debugger because .Result throws an exception. If I press F5, resultTask faults as expected, but it smells.

Is there any way to let resultTask to have the same outcome as someTask if someTask faults?

---

Essentially what I'm trying to do is to express something like this with tasks:

int F()
{
    throw new SomeException();
}

string G(int x)
{
    return x.ToString();
}

try
{
    string result = G(F());
}
catch (SomeException e)
{
    ...
}

Answer 1

I suspect the original exception will be in the AggregateException within the AggregateException if you see what I mean - you just need to unwrap twice, or call AggregateException.Flatten() on the outer AggregateException.