How to flatten a Try[Option[T]] - scala

Question

I want to flatten a Try[Option[T]] into a Try[T]
Here is my code
def flattenTry[T](t: Try[Option[T]]) : Try[T] = {
t match {
case f : Failure[T] => f.asInstanceOf[Failure[T]]
case Success(e) =>
e match {
case None => Failure[T](new Exception("Parsing error"))
case Some(s) => Success(s)
}
}
}
Is there a better way ?

Answer 1

You could try something like this which is a little neater:
val t = Try(Some(1))
val tt = t.flatMap{
case Some(i) => Success(i)
case None => Failure(new Exception("parsing error"))
}
More generically, this would be:
def flattenTry[T](t: Try[Option[T]]) : Try[T] = {
t.flatMap{
case Some(s) => Success(s)
case None => Failure(new Exception("parsing error"))
}
}
The trick is to convert the Option into Try for using flatmap.

Answer 2

Using getOrElse, you could also write:
def flattenTry[T](t: Try[Option[T]]): Try[T] = {
t flatMap { o => o map (Success(_)) getOrElse Failure(new Exception("parsing error")) }
}
You could make this even shorter, but possibly at the cost of functional purity (throwing is a side-effect) and performance (due to throwing/catching):
def flattenTry[T](t: Try[Option[T]]): Try[T] = {
Try(t.get getOrElse { throw new Exception("parsing error") })
}

Answer 3

One possible way is to use Try(o.get) to convert o: Option to o: Try.
This is very concise, but throws and catches exception when handling None, which might perhaps be a performance concern sometimes (or sometimes an ideological / code rules concern). Still, the code is so concise and well readable I think it is worth mentioning:
def flattenTry[T](t: Try[Option[T]]) : Try[T] = {
t.flatMap(o => Try(o.get))
}
Note: not that I recommend using it, but for completeness: even a shorter version is possible, which throws / catches even when Try is a failure:
def flattenTry[T](t: Try[Option[T]]) : Try[T] = {
Try(t.get.get)
}