Scala while(true) type mismatch? Infinite loop in scala?

Question

Why following code

def doSomething() = "Something"

var availableRetries: Int = 10

def process(): String = {
  while (true) {
    availableRetries -= 1
    try {
      return doSomething()
    } catch {
      case e: Exception => {
        if (availableRetries < 0) {
          throw e
        }
      }
    }
  }
}

produces following compiler error

error: type mismatch;
 found   : Unit
 required: String
             while (true) {
             ^

?

This works ok in C#. The while loops forever, so it cannot terminate, therefore it cannot result something else than string. Or how to make infinite loop in Scala?

Answer 1

Functional way to define an infinite loop is recursion:

@annotation.tailrec def process(availableRetries: Int): String = {
  try {
    return doSomething()
  } catch {
    case e: Exception => {
      if (availableRetries < 0) {
        throw e
      }
    }
  }
  return process(availableRetries - 1)
}

elbowich's retry function without inner loop function:

import scala.annotation.tailrec 
import scala.util.control.Exception._ 

@tailrec def retry[A](times: Int)(body: => A): Either[Throwable, A] = { 
  allCatch.either(body) match { 
    case Left(_) if times > 1 => retry(times - 1)(body) 
    case x => x 
  } 
}