Scala 3/scala.util/Try

Try

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. 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.

Companion:
object
Source:
Try.scala
trait Product
trait Equals
class Object
trait Matchable
class Any
class Failure[T]
class Success[T]

Type members

Classlikes

final class WithFilter(p: T => Boolean)

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.

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.

Source:
Try.scala

Value members

Abstract methods

def collect[U](pf: PartialFunction[T, U]): Try[U]

Applies the given partial function to the value from this Success or returns this if this is a Failure.

Applies the given partial function to the value from this Success or returns this if this is a Failure.

Source:
Try.scala
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.

Source:
Try.scala
def filter(p: T => Boolean): Try[T]

Converts this to a Failure if the predicate is not satisfied.

Converts this to a Failure if the predicate is not satisfied.

Source:
Try.scala
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.

Returns the given function applied to the value from this Success or returns this if this is a Failure.

Source:
Try.scala
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].

Transforms a nested Try, ie, a Try of type Try[Try[T]], into an un-nested Try, ie, a Try of type Try[T].

Source:
Try.scala
def fold[U](fa: Throwable => U, fb: T => U): U

Applies fa if this is a Failure or fb if this is a Success.

Applies fa if this is a Failure or fb if this is a Success. If fb is initially applied and throws an exception, then fa is applied with this exception.

Value parameters:
fa

the function to apply if this is a Failure

fb

the function to apply if this is a Success

Returns:

the results of applying the function

Example:

val result: Try[Int] = Try { string.toInt }
log(result.fold(
 ex => "Operation failed with " + ex,
 v => "Operation produced value: " + v
))
Source:
Try.scala
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.

Source:
Try.scala
def get: T

Returns the value from this Success or throws the exception if this is a Failure.

Returns the value from this Success or throws the exception if this is a Failure.

Source:
Try.scala
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.

Source:
Try.scala
def isFailure: Boolean

Returns true if the Try is a Failure, false otherwise.

Returns true if the Try is a Failure, false otherwise.

Source:
Try.scala
def isSuccess: Boolean

Returns true if the Try is a Success, false otherwise.

Returns true if the Try is a Success, false otherwise.

Source:
Try.scala
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.

Maps the given function to the value from this Success or returns this if this is a Failure.

Source:
Try.scala
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.

Returns this Try if it's a Success or the given default argument if this is a Failure.

Source:
Try.scala
def recover[U >: T](pf: 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.

Source:
Try.scala
def recoverWith[U >: T](pf: 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.

Source:
Try.scala
def toEither: Either[Throwable, T]

Returns Left with Throwable if this is a Failure, otherwise returns Right with Success value.

Returns Left with Throwable if this is a Failure, otherwise returns Right with Success value.

Source:
Try.scala
def toOption: Option[T]

Returns None if this is a Failure or a Some containing the value if this is a Success.

Returns None if this is a Failure or a Some containing the value if this is a Success.

Source:
Try.scala
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.

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.

Source:
Try.scala

Concrete methods

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.

Value parameters:
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.

Source:
Try.scala

Inherited methods

def canEqual(that: Any): Boolean

A method that should be called from every well-designed equals method that is open to be overridden in a subclass.

A method that should be called from every well-designed equals method that is open to be overridden in a subclass. See Programming in Scala, Chapter 28 for discussion and design.

Value parameters:
that

the value being probed for possible equality

Returns:

true if this instance can possibly equal that, otherwise false

Inherited from:
Equals
Source:
Equals.scala
def productArity: Int

The size of this product.

The size of this product.

Returns:

for a product A(x1, ..., xk), returns k

Inherited from:
Product
Source:
Product.scala
def productElement(n: Int): Any

The nth element of this product, 0-based.

The nth element of this product, 0-based. In other words, for a product A(x1, ..., xk), returns x(n+1) where 0 <= n < k.

Value parameters:
n

the index of the element to return

Returns:

the element n elements after the first element

Throws:
IndexOutOfBoundsException

if the n is out of range(n < 0 || n >= productArity).

Inherited from:
Product
Source:
Product.scala
def productElementName(n: Int): String

The name of the nth element of this product, 0-based.

The name of the nth element of this product, 0-based. In the default implementation, an empty string.

Value parameters:
n

the index of the element name to return

Returns:

the name of the specified element

Throws:
IndexOutOfBoundsException

if the n is out of range(n < 0 || n >= productArity).

Inherited from:
Product
Source:
Product.scala
def productElementNames: Iterator[String]

An iterator over the names of all the elements of this product.

An iterator over the names of all the elements of this product.

Inherited from:
Product
Source:
Product.scala
def productIterator: Iterator[Any]

An iterator over all the elements of this product.

An iterator over all the elements of this product.

Returns:

in the default implementation, an Iterator[Any]

Inherited from:
Product
Source:
Product.scala
def productPrefix: String

A string used in the toString methods of derived classes.

A string used in the toString methods of derived classes. Implementations may override this method to prepend a string prefix to the result of toString methods.

Returns:

in the default implementation, the empty string

Inherited from:
Product
Source:
Product.scala