Loaner Pattern in Scala

Question

Scala in Depth demonstrates the Loaner Pattern:

def readFile[T](f: File)(handler: FileInputStream => T): T = {
  val resource = new java.io.FileI         


        

Answer 1

With the Loan pattern it is important to know when the "bit" of code that is going to actually call your loaned resource is going to use it.

If you want to return a future from a loan pattern I advise to not create it inside the function that is passed to the loan pattern function.

Don't write

readFile("text.file")(future { doSomething })

but do:

future { readFile("text.file")( doSomething ) }

what I usually do is that I define two types of loan pattern functions: Synchronous and Async

So in your case I would have:

def asyncReadFile[T](f: File)(handler: FileInputStream => T): Future[T] = {
  future{
    readFile(f)(handler)
  }
}

This way you avoid calling closed resources. And you reuse your already tested and hopefully correct code of the Synchronous function.