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
- Alphabetic
- By Inheritance
- Try
- Serializable
- Serializable
- Product
- Equals
- AnyRef
- Any
- by any2stringadd
- by StringFormat
- by Ensuring
- by ArrowAssoc
- Hide All
- Show All
- Public
- All
Type Members
-
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
-
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[Throwable, 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
-
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
-
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
-
final
def
##(): Int
Equivalent to
x.hashCode
except for boxed numeric types andnull
.Equivalent to
x.hashCode
except for boxed numeric types andnull
. 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. Fornull
returns a hashcode wherenull.hashCode
throws aNullPointerException
.- 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] to any2stringadd[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] to ArrowAssoc[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 toif (x eq null) that eq null else x.equals(that)
.The expression
x == that
is equivalent toif (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
.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 aClassCastException
at runtime, while the expressionList(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 typeT0
.
-
def
clone(): AnyRef
Create a copy of the receiver object.
-
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
-
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
-
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
-
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
-
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 ofAnyRef
, and has three additional properties:- It is consistent: for any non-null instances
x
andy
of typeAnyRef
, multiple invocations ofx.eq(y)
consistently returnstrue
or consistently returnsfalse
. - For any non-null instance
x
of typeAnyRef
,x.eq(null)
andnull.eq(x)
returnsfalse
. null.eq(null)
returnstrue
.
When overriding the
equals
orhashCode
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
- It is consistent: for any non-null instances
-
def
equals(arg0: Any): Boolean
The equality method for reference types.
-
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 betweenfinalize
and non-local returns and exceptions, are all platform dependent.- Attributes
- protected[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.Returns string formatted according to given
format
string. Format strings are as forString.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()
-
final
def
getClass(): Class[_]
Returns the runtime class representation of the object.
-
def
hashCode(): Int
The hashCode method for reference types.
-
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 returnfalse
, while the expressionList(1).isInstanceOf[List[String]]
will returntrue
. 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 typeT0
;false
otherwise.
- Definition Classes
- Any
-
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
-
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
-
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
-
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
synchronized[T0](arg0: ⇒ T0): T0
- Definition Classes
- AnyRef
-
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
-
final
def
wait(): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws( ... )
-
final
def
wait(arg0: Long, arg1: Int): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws( ... )
- final def wait(arg0: Long): Unit
-
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()
-
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
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.collection.parallel.immutable
- Immutable, parallel data-structures such asParVector
,ParRange
,ParHashMap
orParHashSet
scala.collection.parallel.mutable
- Mutable, parallel data-structures such asParArray
,ParHashMap
,ParTrieMap
orParHashSet
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.swing
- A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)scala.util.parsing
- Parser combinators (scala-parser-combinators.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
.