on 19-Dec-2014 (Fri)

How to fix this compilation error?
scala> val f = _ + _
<console>:4: error: missing parameter type for expanded
function ((x$1, x$2) => x$1.$plus(x$2))
   val f = _ + _

def echo(args: String*) =
  for (arg <- args) println(arg)

def printTime(out: java.io.PrintStream) =
  out.println("time = "+ System.currentTimeMillis())

def printTime(out: java.io.PrintStream = Console.out) =
  out.println("time = "+ System.currentTimeMillis())

def filesMatching(query: String,
    matcher: (String, String) => Boolean) = {
  for (file <- filesHere; if matcher(file.getName, query))
    yield file
}

def filesEnding(query: String) =
  filesMatching(query, (fileName: String, query: String) => fileName.endsWith(query))

def filesMatching(query: String,
    matcher: (String, String) => Boolean) = {
  for (file <- filesHere; if matcher(file.getName, query))
    yield file
}

def filesEnding(query: String) =
  filesMatching(query, _.endsWith(_))

def filesEnding(query: String) =
  filesMatching(query, _.endsWith(_))

def filesMatching(query: String,
    matcher: (String, String) => Boolean) = {
  for (file <- filesHere; if matcher(file.getName, query))
    yield file
}

def filesEnding(query: String) =
  filesMatching(_.endsWith(query))

def filesMatching(matcher: String => Boolean) =
  for (file <- filesHere; if matcher(file.getName))
    yield file

scala> def plainOldSum(x: Int, y: Int) = x + y
plainOldSum: (x: Int,y: Int)Int
scala> plainOldSum(1, 2)
res4: Int = 3

scala> def curriedSum(x: Int)(y: Int) = x + y
curriedSum: (x: Int)(y: Int)Int
scala> curriedSum(1)(2)
res5: Int = 3

val file = new File("date.txt")
withPrintWriter(file) {
  writer => writer.println(new java.util.Date)
}

def withPrintWriter(file: File)(op: PrintWriter => Unit) {
  // ...
}

def myAssert(predicate: () => Boolean) =
  if (!predicate())
    throw new AssertionError
    
myAssert(() => 5 > 3)

change type () => Boolean to => Boolean:
def myAssert(predicate: => Boolean) =
  if (!predicate())
    throw new AssertionError

myAssert(5 > 3)

class ArrayElement(conts: Array[String]) extends Element {
  val contents: Array[String] = conts
}

class ArrayElement(
  val contents: Array[String]
) extends Element

class LineElement(s: String) extends ArrayElement(Array(s)) {
  // ...
}

trait Doubling extends IntQueue {
  // whatever
}

trait Doubling extends IntQueue {
  abstract override def put(x: Int) { super.put(2 * x) }
}

abstract class Fruit(
  val name: String,
  val color: String
)

def showFruit(fruit: Fruit) {
  import fruit._
  // rest of the method
}

class Outer {
 class Inner {
  private def f() { println("f") }
  class InnerMost {
   f()
  }
 }
 (new Inner).f() // is it legal in Scala? why? woudl it be legal in Java?
}

class Outer {
 class Inner {
  private def f() { println("f") }
  class InnerMost {
   f() // is it legal in Scala? why? would it be legal in Java?
  }
 }
 (new Inner).f() // warning - illegal!
}

package object rocket {
  // definitions go here
}