Scala Standard Library2.13.9 < Back


# 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
-  object Either extends java.io.Serializable
  Definition Classes
    util
- LeftProjection
- MergeableEither
- RightProjection

c

scala.util.Either

# LeftProjection

###

#### final case class LeftProjection[+A, +B](e: Either[A, B]) extends Product with Serializable

Projects an `Either` into a `Left`.

Source
  Either.scala
See also

  scala.util.Either#left

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

1. Alphabetic
2. By Inheritance

Inherited

1. LeftProjection
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

### Instance Constructors

1.  new LeftProjection(e: Either[A, B])

### 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 LeftProjection[A, B] toany2stringadd[LeftProjection[A, B]] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd
4.  def ->[B](y: B): (LeftProjection[A, B], B)
   Implicit
     This member is added by an implicit conversion from LeftProjection[A, B] toArrowAssoc[LeftProjection[A, B]] 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.  val e: Either[A, B]
9.  def ensuring(cond: (LeftProjection[A, B]) => Boolean, msg: => Any): LeftProjection[A, B]
   Implicit
     This member is added by an implicit conversion from LeftProjection[A, B] toEnsuring[LeftProjection[A, B]] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
10.  def ensuring(cond: (LeftProjection[A, B]) => Boolean): LeftProjection[A, B]
    Implicit
      This member is added by an implicit conversion from LeftProjection[A, B] toEnsuring[LeftProjection[A, B]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
11.  def ensuring(cond: Boolean, msg: => Any): LeftProjection[A, B]
    Implicit
      This member is added by an implicit conversion from LeftProjection[A, B] toEnsuring[LeftProjection[A, B]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
12.  def ensuring(cond: Boolean): LeftProjection[A, B]
    Implicit
      This member is added by an implicit conversion from LeftProjection[A, B] toEnsuring[LeftProjection[A, B]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
13.  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
14.  def exists(p: (A) => Boolean): Boolean

    Returns `false` if `Right` or returns the result of the application of the given function to the `Left` value.

    Returns `false` if `Right` or returns the result of the application of the given function to the `Left` value.

        Left(12).left.exists(_ > 10)  // true
        Left(7).left.exists(_ > 10)   // false
        Right(12).left.exists(_ > 10) // false

15.  def filterToOption[B1](p: (A) => Boolean): Option[Either[A, B1]]

    Returns `None` if this is a `Right` or if the given predicate `p` does not hold for the left value, otherwise, returns a `Left`.

    Returns `None` if this is a `Right` or if the given predicate `p` does not hold for the left value, otherwise, returns a `Left`.

        Left(12).left.filterToOption(_ > 10)  // Some(Left(12))
        Left(7).left.filterToOption(_ > 10)   // None
        Right(12).left.filterToOption(_ > 10) // None

16.  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

17.  def flatMap[A1, B1 >: B](f: (A) => Either[A1, B1]): Either[A1, B1]

    Binds the given function across `Left`.

    Binds the given function across `Left`.

        Left(12).left.flatMap(x => Left("scala")) // Left("scala")
        Right(12).left.flatMap(x => Left("scala")) // Right(12)

    f

      The function to bind across `Left`.

18.  def forall(p: (A) => Boolean): Boolean

    Returns `true` if `Right` or returns the result of the application of the given function to the `Left` value.

    Returns `true` if `Right` or returns the result of the application of the given function to the `Left` value.

        Left(12).left.forall(_ > 10)  // true
        Left(7).left.forall(_ > 10)   // false
        Right(12).left.forall(_ > 10) // true

19.  def foreach[U](f: (A) => U): Unit

    Executes the given side-effecting function if this is a `Left`.

    Executes the given side-effecting function if this is a `Left`.

        Left(12).left.foreach(x => println(x))  // prints "12"
        Right(12).left.foreach(x => println(x)) // doesn't print

    f

      The side-effecting function to execute.

20.  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()
21.  def getOrElse[A1 >: A](or: => A1): A1

    Returns the value from this `Left` or the given argument if this is a `Right`.

    Returns the value from this `Left` or the given argument if this is a `Right`.

        Left(12).left.getOrElse(17)  // 12
        Right(12).left.getOrElse(17) // 17

22.  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 returns `true` if the value of the receiver object is a `BigDecimal` or a subtype of `BigDecimal`.
    - `T0` is a parameterized class type, e.g. `List[Int]`: this method returns `true` if the value of the receiver object is some `List[X]` for any `X`. For example, `List(1, 2, 3).isInstanceOf[List[String]]` will return true.
    - `T0` is some singleton type `x.type` or literal `x`: this method returns `this.eq(x)`. For example, `x.isInstanceOf[1]` is equivalent to `x.eq(1)`
    - `T0` is an intersection `X with Y` or `X & Y: this method is equivalent to` x.isInstanceOf[X] && x.isInstanceOf[Y]``
    - `T0` is a union `X | Y`: this method is equivalent to `x.isInstanceOf[X] || x.isInstanceOf[Y]`
    - `T0` is a type parameter or an abstract type member: this method is equivalent to `isInstanceOf[U]` where `U` is `T0`'s upper bound, `Any` if `T0` is unbounded. For example, `x.isInstanceOf[A]` where `A` is an unbounded type parameter will return true for any value of `x`.

    This is exactly equivalent to the type pattern `_: T0`

    returns

      `true` if the receiver object is an instance of erasure of type `T0`; `false` otherwise.

    Definition Classes
      Any
    Note

      due to the unexpectedness of `List(1, 2, 3).isInstanceOf[List[String]]` returning true and `x.isInstanceOf[A]` where `A` is a type parameter or abstract member returning true, these forms issue a warning.

23.  def map[A1](f: (A) => A1): Either[A1, B]

    Maps the function argument through `Left`.

    Maps the function argument through `Left`.

        Left(12).left.map(_ + 2) // Left(14)
        Right[Int, Int](12).left.map(_ + 2) // Right(12)

24.  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
25.  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

26.  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

27.  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
28.  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
29.  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
30.  def toOption: Option[A]

    Returns a `Some` containing the `Left` value if it exists or a `None` if this is a `Right`.

    Returns a `Some` containing the `Left` value if it exists or a `None` if this is a `Right`.

        Left(12).left.toOption // Some(12)
        Right(12).left.toOption // None

31.  def toSeq: Seq[A]

    Returns a `Seq` containing the `Left` value if it exists or an empty `Seq` if this is a `Right`.

    Returns a `Seq` containing the `Left` value if it exists or an empty `Seq` if this is a `Right`.

        Left(12).left.toSeq // Seq(12)
        Right(12).left.toSeq // Seq()

32.  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

33.  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

34.  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

### Deprecated Value Members

1.  def filter[B1](p: (A) => Boolean): Option[Either[A, B1]]

   Returns `None` if this is a `Right` or if the given predicate `p` does not hold for the left value, otherwise, returns a `Left`.

   Returns `None` if this is a `Right` or if the given predicate `p` does not hold for the left value, otherwise, returns a `Left`.

       Left(12).left.filter(_ > 10)  // Some(Left(12))
       Left(7).left.filter(_ > 10)   // None
       Right(12).left.filter(_ > 10) // None

   Annotations
     @deprecated
   Deprecated

     (Since version 2.13.0) Use `filterToOption`, which more accurately reflects the return type

2.  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 LeftProjection[A, B] toStringFormat[LeftProjection[A, B]] performed by method StringFormat in scala.Predef.
   Definition Classes
     StringFormat
   Annotations
     @deprecated @inline()
   Deprecated

     (Since version 2.12.16) Use `formatString.format(value)` instead of `value.formatted(formatString)`, or use the `f""` string interpolator. In Java 15 and later, `formatted` resolves to the new method in String which has reversed parameters.

3.  def get: A

   Returns the value from this `Left` or throws `NoSuchElementException` if this is a `Right`.

   Returns the value from this `Left` or throws `NoSuchElementException` if this is a `Right`.

       Left(12).left.get  // 12
       Right(12).left.get // NoSuchElementException

   Annotations
     @deprecated
   Deprecated

     (Since version 2.13.0) use `Either.swap.getOrElse` instead

   Exceptions thrown

     `NoSuchElementException` if the projection is scala.util.Right

4.  def →[B](y: B): (LeftProjection[A, B], B)
   Implicit
     This member is added by an implicit conversion from LeftProjection[A, B] toArrowAssoc[LeftProjection[A, B]] 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 fromLeftProjection[A, B] to any2stringadd[LeftProjection[A, B]]

### Inherited by implicit conversion StringFormat fromLeftProjection[A, B] to StringFormat[LeftProjection[A, B]]

### Inherited by implicit conversion Ensuring fromLeftProjection[A, B] to Ensuring[LeftProjection[A, B]]

### Inherited by implicit conversion ArrowAssoc fromLeftProjection[A, B] to ArrowAssoc[LeftProjection[A, B]]

### Ungrouped