CODEWITHSUNDEEP
scala
blue-sky
blue-sky

Reputation: 53806

'not found: type' error

I'm reading 'Programming in scala' and in one of the example when I try to compile it in Eclipse I receive error : 'not found: type ChecksumAccumulator' The type is declared as below. Is the code below correct ?

import scala.collection.mutable.Map

object ChecksumAccumulator {

  private val cache = Map[String, Int]()

  def calculate(s: String): Int = 
    if(cache.contains(s))
      cache(s)
    else {
      val acc = new ChecksumAccumulator
      for(c <- s)
        acc.add(c.toBye)
      val cs = acc.checksum()
      cache += (s -> cs)
      cs
    }
}

Upvotes: 0

Views: 9631

Answers (2)

Krishnadas PC
Krishnadas PC

Reputation: 6519

The problem is that in the book class is defined too early and later in the file ChecksumAccumulator.scala class definition is not there. For a beginner it is enough to mislead and will get stuck. This must be the complete code for the two files.

In ChecksumAccumulator.scala

import scala.collection.mutable.Map
class ChecksumAccumulator {
 private
 var sum = 0
 def add(b: Byte) {
  sum += b
 }
 def checksum(): Int = ~(sum & 0xFF) + 1
}
object ChecksumAccumulator {
 private val cache = Map[String, Int]()
 def calculate(s: String): Int =
  if (cache.contains(s))
   cache(s)
  else {
   val acc = new ChecksumAccumulator
   for (c < -s)
    acc.add(c.toByte)
   val cs = acc.checksum()
   cache += (s -> cs)
   cs
  }
}

In Summer.scala

import ChecksumAccumulator.calculate
object Summer {
 def main(args: Array[String]) {
  for (arg < -args)
   println(arg + ": " + calculate(arg))
 }
}

Then you can compile using.

scalac ChecksumAccumulator.scala Summer.scala

Then run the example with

scala Summer of love

Which will give you the below output:

of: -213
love: -182

Upvotes: 0

Travis Brown
Travis Brown

Reputation: 139038

From Programming in Scala:

The singleton object in this figure is named ChecksumAccumulator, the same name as the class in the previous example. When a singleton object shares the same name with a class, it is called that class's companion object. You must define both the class and its companion object in the same source file. The class is called the companion class of the singleton object.

If you try to compile this code alone, without the ChecksumAccumulator class, you'll get a compiler error because you can't create an instance of a singleton object with new. The book does a great job of explaining how companion objects and classes work together, and since you're already reading it I won't bother adding any further summary here.

Upvotes: 1

Related Questions