Is there some reason to avoid return statements

Question

Sometimes I see chunks of Scala code, with several nested levels of conditionals and matchings, that would be much clearer using an explicit return to exit from the function.

Answer 1

A return may be implemented by throwing an exception, so it may have a certain overhead over the standard way of declaring the result of a method. (Thanks for Kim Stebel for pointing out this is not always, maybe not even often, the case.)

Also, a return on a closure will return from the method in which the closure is defined, and not simply from the closure itself. That makes it both useful for that, and useless for returning a result from closures.

An example of the above:

def find[T](seq: Seq[T], predicate: T => Boolean): Option[T] = {
  seq foreach { elem =>
    if (predicate(elem)) return Some(elem) // returns from find
  }
  None
}

If you still don't understand, elem => if (predicate(elem)) return Some(elem) is the method apply of an anonymous object of that implements Function1 and is passed to foreach as parameter. Remove return from it, and it won't work.

Answer 2

An explicit return breaks the control flow. For example if you have a statement like

if(isAuth(user)) {
 return getProfile(user)
}
else {
 return None
}

the control structure (if) is not finished, which is the reason why I argue it is more confusing. For me this is analogous to a break statement. Additionally Scalas 'everything is a value' principle reduces the need for using explicit returns which leads to less people using a keyword which is only useful for def statements:

// start 
def someString:String = return "somestring"

// def without return 
def someString = "somestring"

// after refactoring
val someString = "somestring"    

You see that the type annotation has to be added and when changing the def to a val it is required to remove the return.

Answer 3

One drawback is that the return type can't be inferred. Everything else is a matter of style. What seems unclear or confusing to you might be perfectly "natural" to someone else.