util

Type Members

1. class DynamicVariable[T] extends AnyRef

   

   DynamicVariables provide a binding mechanism where the current value is found through dynamic scope, but where access to the variable itself is resolved through static scope.

   DynamicVariables provide a binding mechanism where the current value is found through dynamic scope, but where access to the variable itself is resolved through static scope.

   The current value can be retrieved with the value method. New values should be pushed using the withValue method. Values pushed via withValue only stay valid while the withValue's second argument, a parameterless closure, executes. When the second argument finishes, the variable reverts to the previous value.

   someDynamicVariable.withValue(newValue) {
     // ... code called in here that calls value ...
     // ... will be given back the newValue ...
   }

   Each thread gets its own stack of bindings. When a new thread is created, the DynamicVariable gets a copy of the stack of bindings from the parent thread, and from then on the bindings for the new thread are independent of those for the original thread.

   Version

   1.1, 2007-5-21

2. sealed abstract class Either[+A, +B] extends Product with Serializable

   

   Represents a value of one of two possible types (a disjoint union.) Instances of Either are either an instance of scala.util.Left or scala.util.Right.

   Represents a value of one of two possible types (a disjoint union.) Instances of Either are either an instance of scala.util.Left or scala.util.Right.

   A common use of Either is as an alternative to scala.Option for dealing with possible missing values. In this usage, scala.None is replaced with a scala.util.Left which can contain useful information. scala.util.Right takes the place of scala.Some. Convention dictates that Left is used for failure and Right is used for success.

   For example, you could use Either[String, Int] to detect whether a received input is a String or an Int.

   val in = Console.readLine("Type Either a string or an Int: ")
   val result: Either[String,Int] = try {
       Right(in.toInt)
     } catch {
       case e: Exception =>
         Left(in)
   }
   
   println( result match {
     case Right(x) => "You passed me the Int: " + x + ", which I will increment. " + x + " + 1 = " + (x+1)
     case Left(x) => "You passed me the String: " + x
   })

   Projections

   A projection can be used to selectively operate on a value of type Either, depending on whether it is of type Left or Right. For example, to transform an Either using a function, in the case where it's a Left, one can first apply the left projection and invoke map on that projected Either. If a right projection is applied to that Left, the original Left is returned, unmodified.

   val l: Either[String, Int] = Left("flower")
   val r: Either[String, Int] = Right(12)
   l.left.map(_.size): Either[Int, Int] // Left(6)
   r.left.map(_.size): Either[Int, Int] // Right(12)
   l.right.map(_.toDouble): Either[String, Double] // Left("flower")
   r.right.map(_.toDouble): Either[String, Double] // Right(12.0)

   Like with other types which define a map method, the same can be achieved using a for-comprehension:

   for (s <- l.left) yield s.size // Left(6)

   Biasing Either values

   You may also bias Either values, decorating them so they can be operated upon and used in for comprehensions without extracting projections. If we treat Either as analogous to Option, a right-biased Either treats Right instances as good values while Left instances represent failures, more descriptive variations on None. (Either can also be left-biased, but right-biasing is conventional and should be preferred.)

   Biased Either values support pattern matches, variable assignments, and conditionals in for comprehensions, which left- and right-projections do not.

   You can right-bias Either very simply via the following import statement:

   import Either.RightBias._
   
   val a : Either[String,Int] = Right(1)
   val b : Either[String,Int] = Right(99)
   
   for( v <- a; w <- b ) yield v+w          // Right(100)
   for( v <- a; w <- b if v > 10) yield v+w // throws NoSuchElementException

   In order to support filter operations without throwing an Exception upon failure, a right bias may define a left-side token to indicate emptiness.

   val RightBias = Either.RightBias.withEmptyToken[String]("EMPTY")
   import RightBias._
   
   val a : Either[String,Int] = Right(1)
   val b : Either[String,Int] = Right(99)
   
   for( v <- a; w <- b ) yield v+w          // Right(100)
   for( v <- a; w <- b if v > 10) yield v+w // Left(EMPTY)

   For very extensive documentation of biased Either, please see RightBias (or, if you wish to defy convention, LeftBias).

   For documentation of operations supported by biased Either values, see right-biased ops / left-biased ops.

   Version

   1.0, 11/10/2008

   Since

   2.7

3. final case class Failure[+T](exception: Throwable) extends Try[T] with Product with Serializable

   

4. final case class Left[+A, +B](a: A) extends Either[A, B] with Product with Serializable

   

   The left side of the disjoint union, as opposed to the scala.util.Right side.

   The left side of the disjoint union, as opposed to the scala.util.Right side.

   Version

   1.0, 11/10/2008

5. class Random extends Serializable

   

6. final case class Right[+A, +B](b: B) extends Either[A, B] with Product with Serializable

   

   The right side of the disjoint union, as opposed to the scala.util.Left side.

   The right side of the disjoint union, as opposed to the scala.util.Left side.

   Version

   1.0, 11/10/2008

7. final case class Success[+T](value: T) extends Try[T] with Product with Serializable

   

8. sealed abstract class Try[+T] extends Product with Serializable

   

   The Try type represents a computation that may either result in an exception, or return a successfully computed value.

   The Try type represents a computation that may either result in an exception, or return a successfully computed value. It's similar to, but semantically different from the scala.util.Either type.

   Instances of Try[T], are either an instance of scala.util.Success[T] or scala.util.Failure[T].

   For example, Try can be used to perform division on a user-defined input, without the need to do explicit exception-handling in all of the places that an exception might occur.

   Example:

   import scala.util.{Try, Success, Failure}
   
   def divide: Try[Int] = {
     val dividend = Try(Console.readLine("Enter an Int that you'd like to divide:\n").toInt)
     val divisor = Try(Console.readLine("Enter an Int that you'd like to divide by:\n").toInt)
     val problem = dividend.flatMap(x => divisor.map(y => x/y))
     problem match {
       case Success(v) =>
         println("Result of " + dividend.get + "/"+ divisor.get +" is: " + v)
         Success(v)
       case Failure(e) =>
         println("You must've divided by zero or entered something that's not an Int. Try again!")
         println("Info from the exception: " + e.getMessage)
         divide
     }
   }

   An important property of Try shown in the above example is its ability to pipeline, or chain, operations, catching exceptions along the way. The flatMap and map combinators in the above example each essentially pass off either their successfully completed value, wrapped in the Success type for it to be further operated upon by the next combinator in the chain, or the exception wrapped in the Failure type usually to be simply passed on down the chain. Combinators such as rescue and recover are designed to provide some type of default behavior in the case of failure.

   Note: only non-fatal exceptions are caught by the combinators on Try (see scala.util.control.NonFatal). Serious system errors, on the other hand, will be thrown.

   Note:: all Try combinators will catch exceptions and return failure unless otherwise specified in the documentation.

   Try comes to the Scala standard library after years of use as an integral part of Twitter's stack.

   Since

   2.10

9. class MurmurHash[T] extends (T) ⇒ Unit

   

   A class designed to generate well-distributed non-cryptographic hashes.

   A class designed to generate well-distributed non-cryptographic hashes. It is designed to be passed to a collection's foreach method, or can take individual hash values with append. Its own hash code is set equal to the hash code of whatever it is hashing.

   Annotations

   @deprecated

   Deprecated

   (Since version 2.10.0) Use the object MurmurHash3 instead.