Scala Standard Library2.13.8 < 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 collection
  Definition Classes
    scala
-  package concurrent
  Definition Classes
    collection
-  package convert
  Definition Classes
    collection
-  package generic
  Definition Classes
    collection
-  package immutable
  Definition Classes
    collection
-  package mutable
  Definition Classes
    collection
- +:
- :+
- AbstractIndexedSeqView
- AbstractIterable
- AbstractIterator
- AbstractMap
- AbstractMapView
- AbstractSeq
- AbstractSeqView
- AbstractSet
- AbstractView
- AnyStepper
- ArrayOps
- BitSet
- BitSetOps
- BufferedIterator
- BuildFrom
- BuildFromLowPriority1
- BuildFromLowPriority2
- ClassTagIterableFactory
- ClassTagSeqFactory
- DefaultMap
- DoubleStepper
- EvidenceIterableFactory
- EvidenceIterableFactoryDefaults
- Factory
- Hashing
- IndexedSeq
- IndexedSeqOps
- IndexedSeqView
- IntStepper
- Iterable
- IterableFactory
- IterableFactoryDefaults
- IterableOnce
- IterableOnceExtensionMethods
- IterableOnceOps
- IterableOps
- Iterator
- JavaConverters
- LazyZip2
- LazyZip3
- LazyZip4
- LinearSeq
- LinearSeqOps
- LongStepper
- Map
- MapFactory
- MapFactoryDefaults
- MapOps
- MapView
- MapViewFactory
- Searching
- Seq
- SeqFactory
- SeqMap
- SeqOps
- SeqView
- Set
- SetOps
- SortedIterableFactory
- SortedMap
- SortedMapFactory
- SortedMapFactoryDefaults
- SortedMapOps
- SortedOps
- SortedSet
- SortedSetFactoryDefaults
- SortedSetOps
- SpecificIterableFactory
- Stepper
- StepperShape
- StepperShapeLowPriority1
- StepperShapeLowPriority2
- StrictOptimizedClassTagSeqFactory
- StrictOptimizedIterableOps
- StrictOptimizedLinearSeqOps
- StrictOptimizedMapOps
- StrictOptimizedSeqFactory
- StrictOptimizedSeqOps
- StrictOptimizedSetOps
- StrictOptimizedSortedMapOps
- StrictOptimizedSortedSetOps
- StringOps
- StringView
- View
- WithFilter

t

scala.collection

# BuildFrom

###
Companion object BuildFrom

#### trait BuildFrom[-From, -A, +C] extends Any

Builds a collection of type `C` from elements of type `A` when a source collection of type `From` is available. Implicit instances of `BuildFrom` are available for all collection types.

From

  Type of source collection

A

  Type of elements (e.g. `Int`, `Boolean`, etc.)

C

  Type of collection (e.g. `List[Int]`, `TreeMap[Int, String]`, etc.)

Self Type
  BuildFrom[From, A, C]
Annotations
  @implicitNotFound()
Source
  BuildFrom.scala

Linear Supertypes
Any
Type Hierarchy

Ordering

1. Alphabetic
2. By Inheritance

Inherited

1. BuildFrom
2. 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

### Abstract Value Members

1.  abstract def fromSpecific(from: From)(it: IterableOnce[A]): C
2.  abstract 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
     Any
3.  abstract def newBuilder(from: From): Builder[A, C]

   Get a Builder for the collection.

   Get a Builder for the collection. For non-strict collection types this will use an intermediate buffer. Building collections with `fromSpecific` is preferred because it can be lazy for lazy collections.

### 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
     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
     Any
3.  def +(other: String): String
   Implicit
     This member is added by an implicit conversion from BuildFrom[From, A, C] toany2stringadd[BuildFrom[From, A, C]] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd
4.  def ->[B](y: B): (BuildFrom[From, A, C], B)
   Implicit
     This member is added by an implicit conversion from BuildFrom[From, A, C] toArrowAssoc[BuildFrom[From, A, C]] performed by method ArrowAssoc in scala.Predef.
   Definition Classes
     ArrowAssoc
   Annotations
     @inline()
5.  final def ==(arg0: Any): Boolean

   Test two objects for equality.

   Test two objects for equality. 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
     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 ensuring(cond: (BuildFrom[From, A, C]) => Boolean, msg: => Any): BuildFrom[From, A, C]
   Implicit
     This member is added by an implicit conversion from BuildFrom[From, A, C] toEnsuring[BuildFrom[From, A, C]] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
8.  def ensuring(cond: (BuildFrom[From, A, C]) => Boolean): BuildFrom[From, A, C]
   Implicit
     This member is added by an implicit conversion from BuildFrom[From, A, C] toEnsuring[BuildFrom[From, A, C]] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
9.  def ensuring(cond: Boolean, msg: => Any): BuildFrom[From, A, C]
   Implicit
     This member is added by an implicit conversion from BuildFrom[From, A, C] toEnsuring[BuildFrom[From, A, C]] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
10.  def ensuring(cond: Boolean): BuildFrom[From, A, C]
    Implicit
      This member is added by an implicit conversion from BuildFrom[From, A, C] toEnsuring[BuildFrom[From, A, C]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
11.  def equals(arg0: Any): Boolean

    Compares the receiver object (`this`) with the argument object (`that`) for equivalence.

    Compares the receiver object (`this`) with the argument object (`that`) for equivalence.

    Any implementation of this method should be an equivalence relation:

    - It is reflexive: for any instance `x` of type `Any`, `x.equals(x)` should return `true`.
    - It is symmetric: for any instances `x` and `y` of type `Any`, `x.equals(y)` should return `true` if and only if `y.equals(x)` returns `true`.
    - It is transitive: for any instances `x`, `y`, and `z` of type `Any` if `x.equals(y)` returns `true` and `y.equals(z)` returns `true`, then `x.equals(z)` should return `true`.

    If you override this method, you should verify that your implementation remains an equivalence relation. Additionally, when overriding this method it is usually necessary to override `hashCode` to ensure that objects which are "equal" (`o1.equals(o2)` returns `true`) hash to the same scala.Int. (`o1.hashCode.equals(o2.hashCode)`).

    returns

      `true` if the receiver object is equivalent to the argument; `false` otherwise.

    Definition Classes
      Any
12.  def hashCode(): Int

    Calculate a hash code value for the object.

    Calculate a hash code value for the object.

    The default hashing algorithm is platform dependent.

    Note that it is allowed for two objects to have identical hash codes (`o1.hashCode.equals(o2.hashCode)`) yet not be equal (`o1.equals(o2)` returns `false`). A degenerate implementation could always return `0`. However, it is required that if two objects are equal (`o1.equals(o2)` returns `true`) that they have identical hash codes (`o1.hashCode.equals(o2.hashCode)`). Therefore, when overriding this method, be sure to verify that the behavior is consistent with the `equals` method.

    returns

      the hash code value for this object.

    Definition Classes
      Any
13.  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.

14.  def toFactory(from: From): Factory[A, C]

    Partially apply a BuildFrom to a Factory

15.  def toString(): String

    Returns a string representation of the object.

    Returns a string representation of the object.

    The default representation is platform dependent.

    returns

      a string representation of the object.

    Definition Classes
      Any

### Deprecated Value Members

1.  def apply(from: From): Builder[A, C]
   Annotations
     @deprecated @inline()
   Deprecated

     (Since version 2.13.0) Use newBuilder() instead of apply()

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 BuildFrom[From, A, C] toStringFormat[BuildFrom[From, A, C]] 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 →[B](y: B): (BuildFrom[From, A, C], B)
   Implicit
     This member is added by an implicit conversion from BuildFrom[From, A, C] toArrowAssoc[BuildFrom[From, A, C]] 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 Any

### Inherited by implicit conversion any2stringadd fromBuildFrom[From, A, C] to any2stringadd[BuildFrom[From, A, C]]

### Inherited by implicit conversion StringFormat fromBuildFrom[From, A, C] to StringFormat[BuildFrom[From, A, C]]

### Inherited by implicit conversion Ensuring fromBuildFrom[From, A, C] to Ensuring[BuildFrom[From, A, C]]

### Inherited by implicit conversion ArrowAssoc fromBuildFrom[From, A, C] to ArrowAssoc[BuildFrom[From, A, C]]

### Ungrouped