Packages

•  package root

  This is the documentation for the Scala standard library.

  This is the documentation for the Scala standard library.

  Package structure

  The scala package contains core types like Int, Float, Array or Option which are accessible in all Scala compilation units without explicit qualification or imports.

  Notable packages include:

  • scala.collection and its sub-packages contain Scala's collections framework
    • scala.collection.immutable - Immutable, sequential data-structures such as Vector, List, Range, HashMap or HashSet
    • scala.collection.mutable - Mutable, sequential data-structures such as ArrayBuffer, StringBuilder, HashMap or HashSet
    • scala.collection.concurrent - Mutable, concurrent data-structures such as TrieMap
  • scala.concurrent - Primitives for concurrent programming such as Futures and Promises
  • scala.io - Input and output operations
  • scala.math - Basic math functions and additional numeric types like BigInt and BigDecimal
  • scala.sys - Interaction with other processes and the operating system
  • scala.util.matching - Regular expressions

  Other packages exist. See the complete list on the right.

  Additional parts of the standard library are shipped as separate libraries. These include:

  • scala.reflect - Scala's reflection API (scala-reflect.jar)
  • scala.xml - XML parsing, manipulation, and serialization (scala-xml.jar)
  • scala.collection.parallel - Parallel collections (scala-parallel-collections.jar)
  • scala.util.parsing - Parser combinators (scala-parser-combinators.jar)
  • scala.swing - A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)

  Automatic imports

  Identifiers in the scala package and the scala.Predef object are always in scope by default.

  Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example, List is an alias for scala.collection.immutable.List.

  Other aliases refer to classes provided by the underlying platform. For example, on the JVM, String is an alias for java.lang.String.

  Definition Classes

  root

•  package scala

  Core Scala types.

  Core Scala types. They are always available without an explicit import.

  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 files = List("file1.txt", "file2.txt", "file3.txt", "file4.txt")
  val lines: Try[Seq[String]] = Using.Manager { use =>
    // acquire resources
    def mkreader(filename: String) = use(new BufferedReader(new FileReader(filename)))
  
    // use your resources here
    def lines(reader: BufferedReader): Iterator[String] =
      Iterator.continually(reader.readLine()).takeWhile(_ != null)
  
    files.map(mkreader).flatMap(lines)
  }

  Composed or "wrapped" resources may be acquired in order of construction, if "underlying" resources are not closed. Although redundant in this case, here is the previous example with a wrapped call to use:

  def mkreader(filename: String) = use(new BufferedReader(use(new FileReader(filename))))

  Custom resources can be registered on construction by requiring an implicit Manager. This ensures they will be released even if composition fails:

  import scala.util.Using
  
  case class X(x: String)(implicit mgr: Using.Manager) extends AutoCloseable {
    override def close() = println(s"CLOSE $x")
    mgr.acquire(this)
  }
  case class Y(y: String)(x: String)(implicit mgr: Using.Manager) extends AutoCloseable {
    val xres = X(x)
    override def close() = println(s"CLOSE $y")
    // an error during construction releases previously acquired resources
    require(y != null, "y is null")
    mgr.acquire(this)
  }
  
  Using.Manager { implicit mgr =>
    val y = Y("Y")("X")
    println(s"USE $y")
  }
  println {
    Using.Manager { implicit mgr =>
      Y(null)("X")
    }
  } // Failure(java.lang.IllegalArgumentException: requirement failed: y is null)

  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

scala.util.Using

Manager

Companion object Manager