sealed abstract class Try[+T] extends Product with Serializable
The Try
type represents a computation that may fail during evaluation by raising an exception.
It holds either a successfully computed value or the exception that was thrown.
This is similar to the scala.util.Either type, but with different semantics.
Instances of Try[T]
are an instance of either scala.util.Success[T] or scala.util.Failure[T].
For example, consider a computation that performs division on user-defined input.
Try
can reduce or eliminate the need for explicit exception handling in all of the places
where an exception might be thrown.
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.
- Source
- Try.scala
- Alphabetic
- By Inheritance
- Try
- Serializable
- Product
- Equals
- AnyRef
- Any
- by any2stringadd
- by StringFormat
- by Ensuring
- by ArrowAssoc
- Hide All
- Show All
- 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
Checks whether this instance can possibly equal
that
.Checks whether this instance can possibly equal
that
.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
- 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] 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 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
Forces the compiler to treat the receiver object as having type
T0
, even though doing so may violate type safety.Forces the compiler to treat the receiver object as having type
T0
, even though doing so may violate type safety.This method is useful when you believe you have type information the compiler doesn't, and it also isn't possible to check the type at runtime. In such situations, skipping type safety is the only option.
It is platform dependent whether
asInstanceOf
has any effect at runtime. It might do a runtime type test on the erasure ofT0
, insert a conversion (such as boxing/unboxing), fill in a default value, or do nothing at all.In particular,
asInstanceOf
is not a type test. It does **not** mean:this match { case x: T0 => x case _ => throw ClassCastException("...")
Use pattern matching or isInstanceOf for type testing instead.
Situations where
asInstanceOf
is useful:- when flow analysis fails to deduce
T0
automatically - when down-casting a type parameter or an abstract type member (which cannot be checked at runtime due to type erasure) If there is any doubt and you are able to type test instead, you should do so.
Be careful of using
asInstanceOf
whenT0
is a primitive type. WhenT0
is primitive,asInstanceOf
may insert a conversion instead of a type test. If your intent is to convert, use atoT
method (x.toChar
,x.toByte
, etc.).- returns
the receiver object.
- Definition Classes
- Any
- Exceptions thrown
ClassCastException
if the receiver is not an instance of the erasure ofT0
, if that can be checked on this platform
- when flow analysis fails to deduce
- 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.
- 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
).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: AnyRef): 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
- final def getClass(): Class[_ <: AnyRef]
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 has the same erasure as
T0
.Test whether the dynamic type of the receiver object has the same erasure as
T0
.Depending on what
T0
is, the test is done in one of the below ways:T0
is a non-parameterized class type, e.g.BigDecimal
: this method returnstrue
if the value of the receiver object is aBigDecimal
or a subtype ofBigDecimal
.T0
is a parameterized class type, e.g.List[Int]
: this method returnstrue
if the value of the receiver object is someList[X]
for anyX
. For example,List(1, 2, 3).isInstanceOf[List[String]]
will return true.T0
is some singleton typex.type
or literalx
: this method returnsthis.eq(x)
. For example,x.isInstanceOf[1]
is equivalent tox.eq(1)
T0
is an intersectionX with Y
orX & Y: this method is equivalent to
x.isInstanceOf[X] && x.isInstanceOf[Y]T0
is a unionX | Y
: this method is equivalent tox.isInstanceOf[X] || x.isInstanceOf[Y]
T0
is a type parameter or an abstract type member: this method is equivalent toisInstanceOf[U]
whereU
isT0
's upper bound,Any
ifT0
is unbounded. For example,x.isInstanceOf[A]
whereA
is an unbounded type parameter will return true for any value ofx
.
This is exactly equivalent to the type pattern
_: T0
- returns
true
if the receiver object is an instance of erasure of typeT0
;false
otherwise.
- Definition Classes
- Any
- Note
due to the unexpectedness of
List(1, 2, 3).isInstanceOf[List[String]]
returning true andx.isInstanceOf[A]
whereA
is a type parameter or abstract member returning true, these forms issue a warning.
- 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 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 synchronized[T0](arg0: => T0): T0
Executes the code in
body
with an exclusive lock onthis
.Executes the code in
body
with an exclusive lock onthis
.- returns
the result of
body
- 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
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait--.
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
- Note
not specified by SLS as a member of AnyRef
- final def wait(arg0: Long, arg1: Int): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-int-
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
- Note
not specified by SLS as a member of AnyRef
- final def wait(arg0: Long): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-.
- 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()
Deprecated Value Members
- 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] toStringFormat[Try[T]] performed by method StringFormat in scala.Predef.
- Definition Classes
- StringFormat
- Annotations
- @deprecated @inline()
- Deprecated
(Since version 2.12.16) Use
formatString.format(value)
instead ofvalue.formatted(formatString)
, or use thef""
string interpolator. In Java 15 and later,formatted
resolves to the new method in String which has reversed parameters.
- 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
- @deprecated
- Deprecated
(Since version 2.13.0) Use
->
instead. If you still wish to display it as one character, consider using a font with programming ligatures such as Fira Code.
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
.