Is the use of exceptions a bad practice in scala?

error-handling, exception, functional-programming, scala

Solution

The following version uses the fact that the right projection of `Either` is a monad, and is exactly equivalent to your code:

def createApplicationToken(accessToken: AccessToken) = for {
   info <- retrieveProviderInfo(accessToken).right
   user <- User.findOrCreateFromProviderInfo(info).right
   refr <- user.refreshApplicationToken.right
} yield refr.token

And does a much better job of showing off the advantages of `Either`.

More generally, the rules are the same as in Java: use exceptions for exceptional situations. You just might find that you change your definition of exceptional a bit when you're working in this style—e.g., invalid user input isn't really exceptional, a timed-out network request isn't really exceptional, etc.

Right-biased `Either` since Scala 2.12

You can now omit `.right`, so the following code is equivalent since Scala 2.12:

def createApplicationToken(accessToken: AccessToken) = for {
   info <- retrieveProviderInfo(accessToken)
   user <- User.findOrCreateFromProviderInfo(info)
   refr <- user.refreshApplicationToken
} yield refr.token

Problem

I've seen many times pieces of scala code using Option (for simple values) or Either[List[Error], T] for handling errors. this gives place to code like this ``` def createApplicationToken(accessToken: AccessToken): Either[List[Error], ApplicationToken] = { // go to social info provider and fetch information retrieveProviderInfo(accessToken).fold( errors => Left(errors), info => { // try to find user using the info from the provider // if it's not there, create user User.findOrCreateFromProviderInfo(info).fold( errors => Left(errors), user => { // try to create a fresh token and save it to the user user.refreshApplicationToken.fold( errors => Left(errors), user => Right(user.token) ) } ) } ) ``` Which produces a not so nice code nesting, forces you to deal with failures on every step, and also forces you to have all your functions return a Either[...] So I'd like to know if the use of exceptions is discouraged in scala (or functional programming in general) there are any drawbacks in using them (regarding immutability or code concurrency) exceptions are somehow in conflict with the principles or functional programming you can think of a better way to code the given example -- One could avoid the nesting by exiting the function as soon as an error is found using the return statement, but using return is also discouraged in scala...

Original source

Related problems