Try

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.io.StdIn
import scala.util.{Try, Success, Failure}

def divide: Try[Int] = {
  val dividend = Try(StdIn.readLine("Enter an Int that you'd like to divide:\n").toInt)
  val divisor = Try(StdIn.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 recover and recoverWith 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

Linear Supertypes

AnyRef, Any

Known Subclasses

Failure, Success

Type Members

class WithFilter extends AnyRef

We need a whole WithFilter class to honor the "doesn't create a new collection" contract even though it seems unlikely to matter much in a collection with max size 1.

Abstract Value Members

abstract def failed: Try[Throwable]

Inverts this Try.
Inverts this Try. If this is a Failure, returns its exception wrapped in a Success. If this is a Success, returns a Failure containing an UnsupportedOperationException.
abstract def filter(p: (T) ⇒ Boolean): Try[T]

Converts this to a Failure if the predicate is not satisfied.
abstract def flatMap[U](f: (T) ⇒ Try[U]): Try[U]

Returns the given function applied to the value from this Success or returns this if this is a Failure.
abstract def flatten[U](implicit ev: <:<[T, Try[U]]): Try[U]

Transforms a nested Try, ie, a Try of type Try[Try[T]], into an un-nested Try, ie, a Try of type Try[T].
abstract def foreach[U](f: (T) ⇒ U): Unit

Applies the given function f if this is a Success, otherwise returns Unit if this is a Failure.
Applies the given function f if this is a Success, otherwise returns Unit if this is a Failure.
Note: If f throws, then this method may throw an exception.
abstract def get: T

Returns the value from this Success or throws the exception if this is a Failure.
abstract def isFailure: Boolean

Returns true if the Try is a Failure, false otherwise.
abstract def isSuccess: Boolean

Returns true if the Try is a Success, false otherwise.
abstract def map[U](f: (T) ⇒ U): Try[U]

Maps the given function to the value from this Success or returns this if this is a Failure.
abstract def recover[U >: T](f: PartialFunction[Throwable, U]): Try[U]

Applies the given function f if this is a Failure, otherwise returns this if this is a Success.
Applies the given function f if this is a Failure, otherwise returns this if this is a Success. This is like map for the exception.
abstract def recoverWith[U >: T](f: PartialFunction[Throwable, Try[U]]): Try[U]

Applies the given function f if this is a Failure, otherwise returns this if this is a Success.
Applies the given function f if this is a Failure, otherwise returns this if this is a Success. This is like flatMap for the exception.

Concrete Value Members

final def !=(arg0: Any): Boolean

Definition Classes
AnyRef → Any
final def ##(): Int

Definition Classes
AnyRef → Any
final def ==(arg0: Any): Boolean

Definition Classes
AnyRef → Any
final def asInstanceOf[T0]: T0

Definition Classes
Any
def clone(): AnyRef

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( ... )
final def eq(arg0: AnyRef): Boolean

Definition Classes
AnyRef
def equals(arg0: Any): Boolean

Definition Classes
AnyRef → Any
def finalize(): Unit

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( classOf[java.lang.Throwable] )
final def getClass(): Class[_]

Definition Classes
AnyRef → Any
def getOrElse[U >: T](default: ⇒ U): U

Returns the value from this Success or the given default argument if this is a Failure.
Returns the value from this Success or the given default argument if this is a Failure.
Note:: This will throw an exception if it is not a success and default throws an exception.
def hashCode(): Int

Definition Classes
AnyRef → Any
final def isInstanceOf[T0]: Boolean

Definition Classes
Any
final def ne(arg0: AnyRef): Boolean

Definition Classes
AnyRef
final def notify(): Unit

Definition Classes
AnyRef
final def notifyAll(): Unit

Definition Classes
AnyRef
def orElse[U >: T](default: ⇒ Try[U]): Try[U]

Returns this Try if it's a Success or the given default argument if this is a Failure.
final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef
def toOption: Option[T]

Returns None if this is a Failure or a Some containing the value if this is a Success.
def toString(): String

Definition Classes
AnyRef → Any
def transform[U](s: (T) ⇒ Try[U], f: (Throwable) ⇒ Try[U]): Try[U]

Completes this Try by applying the function f to this if this is of type Failure, or conversely, by applying s if this is a Success.
final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long, arg1: Int): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def withFilter(p: (T) ⇒ Boolean): WithFilter

Creates a non-strict filter, which eventually converts this to a Failure if the predicate is not satisfied.
Creates a non-strict filter, which eventually converts this to a Failure if the predicate is not satisfied.
Note: unlike filter, withFilter does not create a new Try. Instead, it restricts the domain of subsequent map, flatMap, foreach, and withFilter operations.
As Try is a one-element collection, this may be a bit overkill, but it's consistent with withFilter on Option and the other collections.
p
the predicate used to test elements.
returns
an object of class WithFilter, which supports map, flatMap, foreach, and withFilter operations. All these operations apply to those elements of this Try which satisfy the predicate p.

Annotations
@inline()

Related Docs: object Try | package util

sealed abstract class Try[+T] extends AnyRef

Type Members

class WithFilter extends AnyRef

Abstract Value Members

abstract def failed: Try[Throwable]

abstract def filter(p: (T) ⇒ Boolean): Try[T]

abstract def flatMap[U](f: (T) ⇒ Try[U]): Try[U]

abstract def flatten[U](implicit ev: <:<[T, Try[U]]): Try[U]

abstract def foreach[U](f: (T) ⇒ U): Unit

abstract def get: T

abstract def isFailure: Boolean

abstract def isSuccess: Boolean

abstract def map[U](f: (T) ⇒ U): Try[U]

abstract def recover[U >: T](f: PartialFunction[Throwable, U]): Try[U]

abstract def recoverWith[U >: T](f: PartialFunction[Throwable, Try[U]]): Try[U]

Concrete Value Members

final def !=(arg0: Any): Boolean

final def ##(): Int

final def ==(arg0: Any): Boolean

final def asInstanceOf[T0]: T0

def clone(): AnyRef

final def eq(arg0: AnyRef): Boolean

def equals(arg0: Any): Boolean

def finalize(): Unit

final def getClass(): Class[_]

def getOrElse[U >: T](default: ⇒ U): U

def hashCode(): Int

final def isInstanceOf[T0]: Boolean

final def ne(arg0: AnyRef): Boolean

final def notify(): Unit

final def notifyAll(): Unit

def orElse[U >: T](default: ⇒ Try[U]): Try[U]

final def synchronized[T0](arg0: ⇒ T0): T0

def toOption: Option[T]

def toString(): String

def transform[U](s: (T) ⇒ Try[U], f: (Throwable) ⇒ Try[U]): Try[U]

final def wait(): Unit

final def wait(arg0: Long, arg1: Int): Unit

final def wait(arg0: Long): Unit

final def withFilter(p: (T) ⇒ Boolean): WithFilter

Inherited from AnyRef

Inherited from Any

Ungrouped