Scala 3 Using - problems when reading from file-CodePudding

In a Scala 3 project, I have a method which returns a Try from a given String

def translate(text: String) : Try[Thing] = ...

and a method which is supposed to read the contents of a file and pass it on to the first method. Here, I want to use Using because as far as I understand, this is the functional way to handle file I/O, and it returns a Try which I need anyway, and it makes sure the used resource is closed:

  def translateFromFile(filepath: String) : Try[Thing] =
    Using(Source.fromFile(filepath).getLines.mkString) match
      case Success(s) => translate(s)
      case Failure(e) => Failure(e)

However, the compiler says

given instance of type scala.util.Using.Releasable[String] was found for parameter evidence$1 of method apply in object Using

Honestly, I don't understand this error message, and I couldn't find any help online. Can someone help? What's the correct way to do this? Thanks!

CodePudding user response：

The error means that you're trying to substitute into Using(...) not something that can be closed but a String.

It should be

def translateFromFile(filepath: String) : Try[Thing] =
  Using(Source.fromFile(filepath)) { s =>
    translate(s.getLines.mkString) match {
      case Success(s) => ???
      case Failure(e) => ???
    }
  }

or just

def translateFromFile(filepath: String) : Try[Thing] =
  Using(Source.fromFile(filepath)) { s =>
    translate(s.getLines.mkString)
  }.flatten

Using(...){s => ...} returns Try and your translate returns Try, so it's Try[Try[...]], that's why .flatten.

There is nothing specific to Scala 3.