never-use-return.md

Never use return

As Scala automatically returns the last expression of a block, you just don't need return.

As the return exit immediately the function, it increase the complexity of the function and may cause some hard-to-understand behaviors.

Moreover, it has some unwanted behaviors, for example inside an anonymous function or a lambda. For example, this code compile fine:

def asStrings(list: Seq[Int]): Seq[String] =
  list.map(i => i.toString)

but not this one:

def asStrings(list: Seq[Int]): Seq[String] =
  list.map(i => return i.toString)
// Error:(2, 32) type mismatch;
// found   : String
// required: Seq[String]
// list.map(i => return i.toString)

neither that one:

def asStrings(list: Seq[Int]): String =
  list.map(i => return i.toString)
// Error:(2, 17) type mismatch;
// found   : Seq[Nothing]
// required: String
// list.map(i => return i.toString)

and not even this one:

def asStrings(list: Seq[Int]): Seq[Nothing] =
  list.map(i => return i.toString)
// Error:(2, 32) type mismatch;
// found   : String
// required: Seq[Nothing]
// list.map(i => return i.toString)

Other references

This rule is also present in other best practice guides:

• Alexandru Nedelcu best practices
• Nicolas Rinaudo best practices