Scala Standard Library2.13.3 < Back
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# Packages

-  package root

  This is the documentation for the Scala standard library.

  This is the documentation for the Scala standard library.

  #### Package structure

  The scala package contains core types like `Int`, `Float`, `Array` or `Option` 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 framework
    - `scala.collection.immutable` - Immutable, sequential data-structures such as `Vector`, `List`, `Range`, `HashMap` or `HashSet`
    - `scala.collection.mutable` - Mutable, sequential data-structures such as `ArrayBuffer`, `StringBuilder`, `HashMap` or `HashSet`
    - `scala.collection.concurrent` - Mutable, concurrent data-structures such as `TrieMap`
  - `scala.concurrent` - Primitives for concurrent programming such as `Futures` and `Promises`
  - `scala.io` - Input and output operations
  - `scala.math` - Basic math functions and additional numeric types like `BigInt` and `BigDecimal`
  - `scala.sys` - Interaction with other processes and the operating system
  - `scala.util.matching` - Regular expressions

  Other 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 for `scala.collection.immutable.List`.

  Other aliases refer to classes provided by the underlying platform. For example, on the JVM, `String` is an alias for `java.lang.String`.

  Definition Classes
    root
-  package scala

  Core Scala types.

  Core Scala types. They are always available without an explicit import.

  Definition Classes
    root
-  package util
  Definition Classes
    scala
-  package control
  Definition Classes
    util
-  package hashing
  Definition Classes
    util
-  package matching
  Definition Classes
    util
- ChainingOps
- ChainingSyntax
- DynamicVariable
- Either
- Failure
- Left
- Properties
- Random
- Right
- Sorting
- Success
- Try
- Using
- chaining

c

scala.util

# Try

###
Companion object Try

#### 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

Linear Supertypes
java.io.Serializable, Product, Equals, AnyRef, Any
Known Subclasses
Failure, Success
Type Hierarchy

Ordering

1. Alphabetic
2. By Inheritance

Inherited

1. Try
2. Serializable
3. Product
4. Equals
5. AnyRef
6. Any

Implicitly

1. by any2stringadd
2. by StringFormat
3. by Ensuring
4. by ArrowAssoc

1. Hide All
2. Show All

Visibility

1. Public
2. Protected

### Type Members

1.  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

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[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

      `IndexOutOfBoundsException` if the `n` is out of range(n < 0 || n >= productArity).

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] toany2stringadd[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] toArrowAssoc[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[lang]
   Definition Classes
     AnyRef
   Annotations
     @throws(classOf[java.lang.CloneNotSupportedException]) @native()
   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] toEnsuring[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] toEnsuring[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] toEnsuring[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] toEnsuring[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: AnyRef): 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[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] toStringFormat[Try[T]] performed by method StringFormat in scala.Predef.
    Definition Classes
      StringFormat
    Annotations
      @inline()
16.  final def getClass(): Class[_ <: AnyRef]

    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 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 the `n` is out of range(n < 0 || n >= productArity).

23.  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
24.  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
25.  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
26.  final def synchronized[T0](arg0: => T0): T0

    Executes the code in `body` with an exclusive lock on `this`.

    Executes the code in `body` with an exclusive lock on `this`.

    returns

      the result of `body`

    Definition Classes
      AnyRef
27.  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
28.  final def wait(): Unit

    See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait--.

    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

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

    See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-int-

    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

30.  final def wait(arg0: Long): Unit

    See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-.

    See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-.

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

      not specified by SLS as a member of AnyRef

31.  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()

### Deprecated Value Members

1.  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.

### Inherited from java.io.Serializable

### Inherited from Product

### Inherited from Equals

### Inherited from AnyRef

### Inherited from Any

### Inherited by implicit conversion any2stringadd fromTry[T] to any2stringadd[Try[T]]

### Inherited by implicit conversion StringFormat fromTry[T] to StringFormat[Try[T]]

### Inherited by implicit conversion Ensuring fromTry[T] to Ensuring[Try[T]]

### Inherited by implicit conversion ArrowAssoc fromTry[T] to ArrowAssoc[Try[T]]

### Ungrouped