Packages

  • package root
    Definition Classes
    root
  • package scala
    Definition Classes
    root
  • package util
    Definition Classes
    scala
  • object Using

    A utility for performing automatic resource management.

    A utility for performing automatic resource management. It can be used to perform an operation using resources, after which it releases the resources in reverse order of their creation.

    Usage

    There are multiple ways to automatically manage resources with Using. If you only need to manage a single resource, the apply method is easiest; it wraps the resource opening, operation, and resource releasing in a Try.

    Example:

    import java.io.{BufferedReader, FileReader}
import scala.util.{Try, Using}

val lines: Try[Seq[String]] =
  Using(new BufferedReader(new FileReader("file.txt"))) { reader =>
    Iterator.continually(reader.readLine()).takeWhile(_ != null).toSeq
  }

    If you need to manage multiple resources, Using.Manager should be used. It allows the managing of arbitrarily many resources, whose creation, use, and release are all wrapped in a Try.

    Example:

    import java.io.{BufferedReader, FileReader}
import scala.util.{Try, Using}

val lines: Try[Seq[String]] = Using.Manager { use =>
  val r1 = use(new BufferedReader(new FileReader("file1.txt")))
  val r2 = use(new BufferedReader(new FileReader("file2.txt")))
  val r3 = use(new BufferedReader(new FileReader("file3.txt")))
  val r4 = use(new BufferedReader(new FileReader("file4.txt")))

  // use your resources here
  def lines(reader: BufferedReader): Iterator[String] =
    Iterator.continually(reader.readLine()).takeWhile(_ != null)

  (lines(r1) ++ lines(r2) ++ lines(r3) ++ lines(r4)).toList
}

    If you wish to avoid wrapping management and operations in a Try, you can use Using.resource, which throws any exceptions that occur.

    Example:

    import java.io.{BufferedReader, FileReader}
import scala.util.Using

val lines: Seq[String] =
  Using.resource(new BufferedReader(new FileReader("file.txt"))) { reader =>
    Iterator.continually(reader.readLine()).takeWhile(_ != null).toSeq
  }

    Suppression Behavior

    If two exceptions are thrown (e.g., by an operation and closing a resource), one of them is re-thrown, and the other is added to it as a suppressed exception. If the two exceptions are of different 'severities' (see below), the one of a higher severity is re-thrown, and the one of a lower severity is added to it as a suppressed exception. If the two exceptions are of the same severity, the one thrown first is re-thrown, and the one thrown second is added to it as a suppressed exception. If an exception is a ControlThrowable, or if it does not support suppression (see Throwable's constructor with an enableSuppression parameter), an exception that would have been suppressed is instead discarded.

    Exceptions are ranked from highest to lowest severity as follows:

    • java.lang.VirtualMachineError
    • java.lang.LinkageError
    • java.lang.InterruptedException and java.lang.ThreadDeath
    • fatal exceptions, excluding scala.util.control.ControlThrowable
    • scala.util.control.ControlThrowable
    • all other exceptions

    When more than two exceptions are thrown, the first two are combined and re-thrown as described above, and each successive exception thrown is combined as it is thrown.

    Definition Classes
    util
  • Manager
  • Releasable

final class Manager extends AnyRef

A resource manager.

Resources can be registered with the manager by calling acquire; such resources will be released in reverse order of their acquisition when the manager is closed, regardless of any exceptions thrown during use.

See the main doc for Using for full details of suppression behavior.

Note

It is recommended for API designers to require an implicit Manager for the creation of custom resources, and to call acquire during those resources' construction. Doing so guarantees that the resource must be automatically managed, and makes it impossible to forget to do so. Example:

class SafeFileReader(file: File)(implicit manager: Using.Manager)
  extends BufferedReader(new FileReader(file)) {

  def this(fileName: String)(implicit manager: Using.Manager) = this(new File(fileName))

  manager.acquire(this)
}
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  4. def acquire[R](resource: R)(implicit arg0: Releasable[R]): Unit

    Registers the specified resource with this manager, so that the resource is released when the manager is closed.

  5. def apply[R](resource: R)(implicit arg0: Releasable[R]): R

    Registers the specified resource with this manager, so that the resource is released when the manager is closed, and then returns the (unmodified) resource.

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