Packages

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
Serializable, java.io.Serializable, Product, Equals, AnyRef, Any
Known Subclasses
Failure, Success
Ordering
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Inherited
  1. Try
  2. Serializable
  3. Serializable
  4. Product
  5. Equals
  6. AnyRef
  7. Any
Implicitly
  1. by any2stringadd
  2. by StringFormat
  3. by Ensuring
  4. by ArrowAssoc
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Visibility
  1. Public
  2. All

Type Members

  1. 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.

    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.

    Annotations
    @deprecatedInheritance( message = ... , since = "2.12.0" )

Abstract Value Members

  1. 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.

    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
  2. abstract 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.

  3. 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.

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

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

  5. 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.

  6. 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].

  7. 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.

    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: 

    1. val result: Try[Throwable, Int] = Try { string.toInt }
log(result.fold(
  ex => "Operation failed with " + ex,
  v => "Operation produced value: " + v
))
  8. 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.

  9. abstract def get: T

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

  10. abstract 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.

  11. abstract def isFailure: Boolean

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

  12. abstract def isSuccess: Boolean

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

  13. 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.

  14. abstract 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.

  15. abstract def productArity: Int

    The size of this product.

    The size of this product.

    returns

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

    Definition Classes
    Product
  16. abstract 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.

    n

    the index of the element to return

    returns

    the element n elements after the first element

    Definition Classes
    Product
    Exceptions thrown
  17. 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.

    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.

  18. 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.

    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.

  19. abstract def toEither: Either[Throwable, T]

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

  20. abstract def toOption: Option[T]

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

  21. abstract 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.

Concrete Value Members

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

    Test two objects for inequality.

    Test two objects for inequality.

    returns

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

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

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

    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
  3. def +(other: String): String
    Implicit
    This member is added by an implicit conversion from Try[T] to any2stringadd[Try[T]] performed by method any2stringadd in scala.Predef.
    Definition Classes
    any2stringadd
  4. def ->[B](y: B): (Try[T], B)
    Implicit
    This member is added by an implicit conversion from Try[T] to ArrowAssoc[Try[T]] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc
    Annotations
    @inline()
  5. final def ==(arg0: Any): Boolean

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

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

    not specified by SLS as a member of AnyRef

  8. def ensuring(cond: (Try[T]) ⇒ Boolean, msg: ⇒ Any): Try[T]
    Implicit
    This member is added by an implicit conversion from Try[T] to Ensuring[Try[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  9. def ensuring(cond: (Try[T]) ⇒ Boolean): Try[T]
    Implicit
    This member is added by an implicit conversion from Try[T] to Ensuring[Try[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  10. def ensuring(cond: Boolean, msg: ⇒ Any): Try[T]
    Implicit
    This member is added by an implicit conversion from Try[T] to Ensuring[Try[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  11. def ensuring(cond: Boolean): Try[T]
    Implicit
    This member is added by an implicit conversion from Try[T] to Ensuring[Try[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  12. final def eq(arg0: AnyRef): Boolean

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

    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
  13. def equals(arg0: Any): Boolean

    The equality method for reference types.

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

    not specified by SLS as a member of AnyRef

  15. def formatted(fmtstr: String): String

    Returns string formatted according to given format 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] to StringFormat[Try[T]] performed by method StringFormat in scala.Predef.
    Definition Classes
    StringFormat
    Annotations
    @inline()
  16. final def getClass(): Class[_]

    Returns the runtime class representation of the object.

    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()
  17. def hashCode(): Int

    The hashCode method for reference types.

    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()
  18. 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
  19. 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
  20. 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
    Annotations
    @native()
    Note

    not specified by SLS as a member of AnyRef

  21. 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
    Annotations
    @native()
    Note

    not specified by SLS as a member of AnyRef

  22. 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]

    Definition Classes
    Product
  23. 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

    Definition Classes
    Product
  24. final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
    AnyRef
  25. 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
  26. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  27. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  28. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
    Annotations
    @native() @throws( ... )
  29. 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()
  30. def →[B](y: B): (Try[T], B)
    Implicit
    This member is added by an implicit conversion from Try[T] to ArrowAssoc[Try[T]] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc

Inherited from Serializable

Inherited from java.io.Serializable

Inherited from Product

Inherited from Equals

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion any2stringadd from Try[T] to any2stringadd[Try[T]]

Inherited by implicit conversion StringFormat from Try[T] to StringFormat[Try[T]]

Inherited by implicit conversion Ensuring from Try[T] to Ensuring[Try[T]]

Inherited by implicit conversion ArrowAssoc from Try[T] to ArrowAssoc[Try[T]]

Ungrouped