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.

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

trait Serializable

trait Product

trait Equals

class Object

trait Matchable

class Any

class Failure[T]

class Success[T]

Type members

Classlikes

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.

Value members

Abstract methods

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

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.

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

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

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

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 Params

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
))

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.

Returns the value from this Success or throws the exception 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.

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

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

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

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

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.

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.

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

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

Concrete methods

@inline

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 Params

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.

Inherited methods

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 Params

that: the value being probed for possible equality

Returns

true if this instance can possibly equal that, otherwise false

Inherited from

Equals

The size of this product.

Returns: for a product A(x1, ..., xk), returns k
Inherited from: Product

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 Params

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

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 Params

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

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

Inherited from: Product

An iterator over all the elements of this product.

Returns: in the default implementation, an Iterator[Any]
Inherited from: Product

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