Newbie question about Either exceptions and coding style

the best would probably be to move the spots that can actually throw exceptions as far away as possible, and wrap them already to return an Either, so you don't need to handle the exceptions in outer instances (you know, make sure connect and close are wrapped to return an Either, as well as the folder create method). and yes, you could also throw an exception when newFolder.create returns false, so that there is only one spot in that method that constructs the Right case.

best, -sciss-

On 7 Jan 2012, at 20:57, smartmobili wrote:

> Hi,
>
> I have started to learn scala a few days ago and I find it very
> interesting even if now I am just managing to stand on my feet and
> still cannot run
> but I hope that in a few month I will feel all the power of this
> language.
> For now my questions are maybe quite simple but I prefer to ask here,
> so I am learning not by reading entire books but by practical examples
> and
> for the moment I am working on a webmail backend with the java mail
> api.
> The method I would like to create is used to create a new folder
> inside a mailbox so at the beginning I didn't know Option, Either, ...
> so I started with this :
>
> def createFolder(folderName: String): List[SMMailbox] = {
> var folders: List[SMMailbox] = List()
>
> try {
> // Connect
> val store: Store = connect
>
> // Get the specified folder
> val newFolder: Folder = store.getFolder(folderName)
> if(! newFolder.exists) {
>
> if(newFolder.create(Folder.HOLDS_MESSAGES)) {
> // creation succeeded - create a list with one SMMailbox
> element
> folders = List(new SMMailbox(folderName, 0, 0))
> }
>
> }
>
> store.close
> } catch {
> case e: Exception => e.printStackTrace();log.info("Cannot
> create folder "+folderName);
> }
>
> folders
> }
>
> This is very naive implementation where when creation succeeds we
> return our object inside a list and if it doesn't the list empty.
> Ok I know this is a bit pathetic but it should work.
> So now I want to improve this method and after discovering Either I am
> writing this :
>
> def createFolder(folderName: String): Either[String,SMMailbox] = {
> var folder :SMMailbox = new SMMailbox(folderName, 0, 0)
>
> try {
> // Connect
> val store: Store = connect
>
> // Get the specified folder
> val newFolder: Folder = store.getFolder(folderName)
> if(! newFolder.exists) {
>
> if(!newFolder.create(Folder.HOLDS_MESSAGES)) {
> // creation didn't succeeded
> Left("Cannot create folder "+folderName)
> }
>
> }
> store.close
>
> Right(new SMMailbox(folderName, 0, 0))
> } catch {
> case e: Exception => e.printStackTrace();Left("Cannot create
> folder "+folderName);
> //case e: NoSuchProviderException => e.printStackTrace();
> log.info("Authentication denied to "); ""
> //case e: MessagingException => e.printStackTrace();
> log.debug("Error found when trying to authenticate "+user);
> stackTrace(e)
> }
> }
>
> So this time to my opinion it looks better but I don't like the fact
> that error handling is done twice, a first time if createFolder failed
> and a second time
> if there was an exception. How can I fix that ? Should I throw an
> exception if the createFolder failed and handle everything in the
> catch ?
> I would like also to add some comments, is there any default coding
> style for comments ?
>
>
> Thanks
>
>
>