Scala saves you lines

Very brief post about Scala programming

Few days ago I played a bit with Scala's fold operations.

I had a list containing rules that all needed to be completed to continue.

Because I have a long history with Java, the first version:

def areRulesCompleted(ruleList:List[Rule]):Boolean= {
  var isCompleted:Boolean = true
ruleList.foreach(rule =>{
    if (!rule.isCompleted) isCompleted = false
  })
  return isCompleted
}

As you can see there's plenty of rows and it's not very functional. Then with foldLeft

ruleList.foldLeft(true)((resolvedValue,rule)=>(resolvedValue && rule.isCompleted))

Better! But we can do it even simpler way

ruleList.foldLeft(true)(_ && _.isCompleted)

so combining this with the method declaration:

def areRulesCompleted(ruleList:List[Rule]) = ruleList.foldLeft(true)(_ && _.isCompleted)

Here's even shorter version (short-circuit) by: Ilkka.

def areRulesCompleted(rules: List[Rule]) = !rules.exists(!_.isCompleted)

I also checked that foldLeft is short-circuiting but foldRight is not.