scala.util

Try

sealed abstract class Try[+T] extends AnyRef

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 Success[T] or 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.

Source
Try.scala
Since

2.10

Linear Supertypes
AnyRef, Any
Known Subclasses
Failure, Success
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Instance Constructors

  1. new Try()

Abstract Value Members

  1. abstract def failed: Try[Throwable]

    Completes this Try with an exception wrapped in a Success.

    Completes this Try with an exception wrapped in a Success. The exception is either the exception that the Try failed with (if a Failure) or an UnsupportedOperationException.

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

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

  3. 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.

  4. 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].

  5. 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.

  6. abstract def get: T

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

  7. abstract def isFailure: Boolean

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

  8. abstract def isSuccess: Boolean

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

  9. 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.

  10. 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.

  11. 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

  1. final def !=(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef

  2. final def !=(arg0: Any): Boolean

    Test two objects for inequality.

    Test two objects for inequality.

    returns

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

    Definition Classes
    Any

  3. final def ##(): Int

    Equivalent to x.hashCode except for boxed numeric types.

    Equivalent to x.hashCode except for boxed numeric types. 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.

    returns

    a hash value consistent with ==

    Definition Classes
    AnyRef → Any

  4. final def ==(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef

  5. final def ==(arg0: Any): Boolean

    Test two objects for equality.

    Test two objects for equality.

    returns

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

    Definition Classes
    Any

  6. final def asInstanceOf[T0]: T0

    Cast the receiver object to be of type 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.

  7. def clone(): AnyRef

    Create a copy of the receiver object.

    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[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws()
    Note

    not specified by SLS as a member of AnyRef

  8. final def eq(arg0: AnyRef): Boolean

    Tests whether the argument (arg0) is a reference to the receiver object (this).

    Tests whether the argument (arg0) 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

  9. def equals(arg0: Any): Boolean

    The equality method for reference types.

    The equality method for reference types. See equals in Any.

    returns

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

    Definition Classes
    AnyRef → Any

  10. def finalize(): Unit

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

    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[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws()
    Note

    not specified by SLS as a member of AnyRef

  11. final def getClass(): java.lang.Class[_]

    A representation that corresponds to the dynamic class of the receiver object.

    A representation that corresponds to the dynamic class of the receiver object.

    The nature of the representation is platform dependent.

    returns

    a representation that corresponds to the dynamic class of the receiver object.

    Definition Classes
    AnyRef → Any
    Note

    not specified by SLS as a member of AnyRef

  12. 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.

  13. def hashCode(): Int

    The hashCode method for reference types.

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

    returns

    the hash code value for this object.

    Definition Classes
    AnyRef → Any

  14. final def isInstanceOf[T0]: Boolean

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

    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

  15. final def ne(arg0: AnyRef): Boolean

    Equivalent to !(this eq that).

    Equivalent to !(this eq that).

    returns

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

    Definition Classes
    AnyRef

  16. final def notify(): Unit

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

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

    Definition Classes
    AnyRef
    Note

    not specified by SLS as a member of AnyRef

  17. final def notifyAll(): Unit

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

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

    Definition Classes
    AnyRef
    Note

    not specified by SLS as a member of AnyRef

  18. 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.

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

    Definition Classes
    AnyRef

  20. def toOption: Option[T]

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

  21. def toString(): String

    Creates a String representation of this object.

    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

  22. 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.

  23. final def wait(): Unit

    Definition Classes
    AnyRef
    Annotations
    @throws()

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

    Definition Classes
    AnyRef
    Annotations
    @throws()

  25. final def wait(arg0: Long): Unit

    Definition Classes
    AnyRef
    Annotations
    @throws()

Inherited from AnyRef

Inherited from Any