Class scala.util.Try

Companion object 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.

Source
Try.scala
Since

2.10

Linear Supertypes
java.io.Serializable, Product, Equals, AnyRef, Any
Known Subclasses
Failure, Success

Type Members

final class WithFilter extends AnyRef

Abstract Value Members

abstract 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. See Programming in Scala, Chapter 28 for discussion and design.

that

the value being probed for possible equality

returns

true if this instance can possibly equal that, otherwise false

Definition Classes
Equals

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

abstract def failed: Try[Throwable]

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]

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

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

abstract def fold[U](fa: (Throwable) => U, fb: (T) => U): U

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.

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
))

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.

Note: If f throws, then this method may throw an exception.

abstract def get: T

abstract def getOrElse[U >: T](default: => U): U

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.

abstract def isFailure: Boolean

abstract def isSuccess: Boolean

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

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

abstract def productArity: Int

The size of this product.

returns

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

Definition Classes
Product

abstract def productElement(n: Int): Any

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.

n

the index of the element to return

returns

the element n elements after the first element

Definition Classes
Product
Exceptions thrown

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

abstract 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. This is like map for the exception.

abstract 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. This is like flatMap for the exception.

abstract def toEither: Either[Throwable, T]

abstract def toOption: Option[T]

abstract def transform[U](s: (T) => Try[U], f: (Throwable) => Try[U]): Try[U]

Concrete Value Members

final def !=(arg0: Any): Boolean

Test two objects for inequality.

returns

true if !(this == that), false otherwise.

Definition Classes
AnyRef → Any

final def ##(): Int

Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.

returns

a hash value consistent with ==

Definition Classes
AnyRef → Any

def +(other: String): String

Implicit
This member is added by an implicit conversion from Try[T] toany2stringadd[Try[T]] performed by method any2stringadd in scala.Predef.
Definition Classes
any2stringadd

def ->[B](y: B): (Try[T], B)

Implicit
This member is added by an implicit conversion from Try[T] toArrowAssoc[Try[T]] performed by method ArrowAssoc in scala.Predef.
Definition Classes
ArrowAssoc
Annotations
@inline()

final def ==(arg0: Any): Boolean

The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

returns

true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
AnyRef → Any

final def asInstanceOf[T0]: T0

Cast the receiver object to be of type T0.

Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.

returns

the receiver object.

Definition Classes
Any
Exceptions thrown

ClassCastException if the receiver object is not an instance of the erasure of type T0.

def clone(): AnyRef

Create a copy of the receiver object.

The default implementation of the clone method is platform dependent.

returns

a copy of the receiver object.

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.CloneNotSupportedException]) @native()
Note

not specified by SLS as a member of AnyRef

def ensuring(cond: (Try[T]) => Boolean, msg: => Any): Try[T]

Implicit
This member is added by an implicit conversion from Try[T] toEnsuring[Try[T]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

def ensuring(cond: (Try[T]) => Boolean): Try[T]

Implicit
This member is added by an implicit conversion from Try[T] toEnsuring[Try[T]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

def ensuring(cond: Boolean, msg: => Any): Try[T]

Implicit
This member is added by an implicit conversion from Try[T] toEnsuring[Try[T]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

def ensuring(cond: Boolean): Try[T]

Implicit
This member is added by an implicit conversion from Try[T] toEnsuring[Try[T]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

final def eq(arg0: AnyRef): Boolean

Tests whether the argument (that) is a reference to the receiver object (this).

The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:

    It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false. null.eq(null) returns true.

When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).

returns

true if the argument is a reference to the receiver object; false otherwise.

Definition Classes
AnyRef

def equals(arg0: AnyRef): Boolean

The equality method for reference types. Default implementation delegates to eq.

See also equals in scala.Any.

returns

true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
AnyRef → Any

def finalize(): Unit

Called by the garbage collector on the receiver object when there are no more references to the object.

The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.Throwable])
Note

not specified by SLS as a member of AnyRef

def formatted(fmtstr: String): String

Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).

Implicit
This member is added by an implicit conversion from Try[T] toStringFormat[Try[T]] performed by method StringFormat in scala.Predef.
Definition Classes
StringFormat
Annotations
@inline()

final def getClass(): Class[_ <: AnyRef]

Returns the runtime class representation of the object.

returns

a class object corresponding to the runtime type of the receiver.

Definition Classes
AnyRef → Any
Annotations
@native()

def hashCode(): Int

The hashCode method for reference types. See hashCode in scala.Any.

returns

the hash code value for this object.

Definition Classes
AnyRef → Any
Annotations
@native()

final def isInstanceOf[T0]: Boolean

Test whether the dynamic type of the receiver object is T0.

Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.

returns

true if the receiver object is an instance of erasure of type T0; false otherwise.

Definition Classes
Any

final def ne(arg0: AnyRef): Boolean

Equivalent to !(this eq that).

returns

true if the argument is not a reference to the receiver object; false otherwise.

Definition Classes
AnyRef

final def notify(): Unit

Wakes up a single thread that is waiting on the receiver object's monitor.

Definition Classes
AnyRef
Annotations
@native()
Note

not specified by SLS as a member of AnyRef

final def notifyAll(): Unit

Wakes up all threads that are waiting on the receiver object's monitor.

Definition Classes
AnyRef
Annotations
@native()
Note

not specified by SLS as a member of AnyRef

def productElementName(n: Int): String

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

n

the index of the element name to return

returns

the name of the specified element

Definition Classes
Product
Exceptions thrown

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

def productElementNames: Iterator[String]

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

Definition Classes
Product

def productIterator: Iterator[Any]

An iterator over all the elements of this product.

returns

in the default implementation, an Iterator[Any]

Definition Classes
Product

def productPrefix: String

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

Definition Classes
Product

final def synchronized[T0](arg0: => T0): T0

Definition Classes
AnyRef

def toString(): String

Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.

returns

a String representation of the object.

Definition Classes
AnyRef → Any

final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

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

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException]) @native()

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.

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()

© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.13.0/scala/util/Try.html