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
- Alphabetic
- By Inheritance
- Try
- Serializable
- Product
- Equals
- AnyRef
- Any
- by any2stringadd
- by StringFormat
- by Ensuring
- by ArrowAssoc
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- Public
- Protected
Type Members
- final 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.
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.
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]
Applies the given partial function to the value from this
Success
or returns this if this is aFailure
. - abstract def failed: Try[Throwable]
Inverts this
Try
.Inverts this
Try
. If this is aFailure
, returns its exception wrapped in aSuccess
. If this is aSuccess
, returns aFailure
containing anUnsupportedOperationException
. - abstract def filter(p: (T) => Boolean): Try[T]
Converts this to a
Failure
if the predicate is not satisfied. - 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 aFailure
. - abstract def flatten[U](implicit ev: <:<[T, Try[U]]): Try[U]
Transforms a nested
Try
, ie, aTry
of typeTry[Try[T]]
, into an un-nestedTry
, ie, aTry
of typeTry[T]
. - abstract def fold[U](fa: (Throwable) => U, fb: (T) => U): U
Applies
fa
if this is aFailure
orfb
if this is aSuccess
.Applies
fa
if this is aFailure
orfb
if this is aSuccess
. Iffb
is initially applied and throws an exception, thenfa
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
val result: Try[Int] = Try { string.toInt } log(result.fold( ex => "Operation failed with " + ex, v => "Operation produced value: " + v ))
Example: - abstract def foreach[U](f: (T) => U): Unit
Applies the given function
f
if this is aSuccess
, otherwise returnsUnit
if this is aFailure
.Applies the given function
f
if this is aSuccess
, otherwise returnsUnit
if this is aFailure
.Note: If
f
throws, then this method may throw an exception. - abstract def get: T
Returns the value from this
Success
or throws the exception if this is aFailure
. - abstract def getOrElse[U >: T](default: => U): U
Returns the value from this
Success
or the givendefault
argument if this is aFailure
.Returns the value from this
Success
or the givendefault
argument if this is aFailure
.Note:: This will throw an exception if it is not a success and default throws an exception.
- abstract def isFailure: Boolean
Returns
true
if theTry
is aFailure
,false
otherwise. - abstract def isSuccess: Boolean
Returns
true
if theTry
is aSuccess
,false
otherwise. - 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 aFailure
. - abstract def orElse[U >: T](default: => Try[U]): Try[U]
Returns this
Try
if it's aSuccess
or the givendefault
argument if this is aFailure
. - abstract def productArity: Int
The size of this product.
- 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)
, returnsx(n+1)
where0 <= 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 then
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 aFailure
, otherwise returns this if this is aSuccess
.Applies the given function
f
if this is aFailure
, otherwise returns this if this is aSuccess
. 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 aFailure
, otherwise returns this if this is aSuccess
.Applies the given function
f
if this is aFailure
, otherwise returns this if this is aSuccess
. This is likeflatMap
for the exception. - abstract def toEither: Either[Throwable, T]
Returns
Left
withThrowable
if this is aFailure
, otherwise returnsRight
withSuccess
value. - abstract def toOption: Option[T]
Returns
None
if this is aFailure
or aSome
containing the value if this is aSuccess
. - abstract def transform[U](s: (T) => Try[U], f: (Throwable) => Try[U]): Try[U]
Completes this
Try
by applying the functionf
to this if this is of typeFailure
, or conversely, by applyings
if this is aSuccess
.
Concrete Value Members
- 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.
- n
the index of the element name to return
- returns
the name of the specified element
- Definition Classes
- Product
- Exceptions thrown
IndexOutOfBoundsException
if then
is out of range(n < 0 || n >= productArity).
- 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.
- Definition Classes
- Product
- 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
- 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 oftoString
methods.- returns
in the default implementation, the empty string
- Definition Classes
- Product
- 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
, andwithFilter
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 supportsmap
,flatMap
,foreach
, andwithFilter
operations. All these operations apply to those elements of this Try which satisfy the predicatep
.
- Annotations
- @inline()
This is the documentation for the Scala standard library.
Package structure
The scala package contains core types like
Int
,Float
,Array
orOption
which are accessible in all Scala compilation units without explicit qualification or imports.Notable packages include:
scala.collection
and its sub-packages contain Scala's collections frameworkscala.collection.immutable
- Immutable, sequential data-structures such asVector
,List
,Range
,HashMap
orHashSet
scala.collection.mutable
- Mutable, sequential data-structures such asArrayBuffer
,StringBuilder
,HashMap
orHashSet
scala.collection.concurrent
- Mutable, concurrent data-structures such asTrieMap
scala.concurrent
- Primitives for concurrent programming such asFutures
andPromises
scala.io
- Input and output operationsscala.math
- Basic math functions and additional numeric types likeBigInt
andBigDecimal
scala.sys
- Interaction with other processes and the operating systemscala.util.matching
- Regular expressionsOther packages exist. See the complete list on the right.
Additional parts of the standard library are shipped as separate libraries. These include:
scala.reflect
- Scala's reflection API (scala-reflect.jar)scala.xml
- XML parsing, manipulation, and serialization (scala-xml.jar)scala.collection.parallel
- Parallel collections (scala-parallel-collections.jar)scala.util.parsing
- Parser combinators (scala-parser-combinators.jar)scala.swing
- A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)Automatic imports
Identifiers in the scala package and the
scala.Predef
object are always in scope by default.Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example,
List
is an alias forscala.collection.immutable.List
.Other aliases refer to classes provided by the underlying platform. For example, on the JVM,
String
is an alias forjava.lang.String
.