Loan pattern

gistfile1.scala

// Purpose:
// - Ensures that a resource is deterministically disposed of once it goes out of scope
// - Use this pattern when working with resources that should be closed or managed after use
//
// The benefit of this pattern is that it frees the developer from the responsibility of
// explicitly managing resources

import scala.io.Source
import java.io._
 
def withFileIterator[A](name: String, encoding: String = "UTF-8")(func: Iterator[String] => A): A = {
  val source = Source.fromFile(name, "UTF-8")
  val lines = source.getLines()
  try {
    func(lines)
  } finally {
    source.close()
  }
}

withFileIterator("greetings.txt") { lines => 
  lines.length
}

def withFileLine[A](name: String, encoding: String = "UTF-8")(func: String => A): Unit = {
  val in = new BufferedReader(new InputStreamReader(new FileInputStream(name), encoding))
  try {
    var line = in.readLine
    while (line != null) {
      func(line)
      line = in.readLine
    }
  } finally {
    in.close
  }
}

withFileLine("greetings.txt")(println)

def withPrintWriter[A](name: String, append: Boolean = true)(func: PrintWriter => A): A = {
  val writer = new PrintWriter(new BufferedWriter(new FileWriter(name, append)))
  try {
    func(writer)
  } finally {
    writer.close()
  }
}

withPrintWriter("greetings.txt") { writer =>
  writer.println("hello world!")
}


// Flattening a Loan Pattern
//
// When loaning several objects, one often ends up with nested functions which can
// be flattened using the pattern here: 
// http://www.casualmiracles.com/2012/04/18/flattening-the-loan-pattern/