scala

# PartialFunction

###
Related Docs: object PartialFunction | package scala

#### trait PartialFunction[-A, +B] extends (A) ⇒ B

A partial function of type `PartialFunction[A, B]` is a unary function where the domain does not necessarily include all values of type `A`. The function `isDefinedAt` allows to test dynamically if a value is in the domain of the function.

Even if `isDefinedAt` returns true for an `a: A`, calling `apply(a)` may still throw an exception, so the following code is legal:

    val f: PartialFunction[Int, Any] = { case _ => 1/0 }

It is the responsibility of the caller to call `isDefinedAt` before calling `apply`, because if `isDefinedAt` is false, it is not guaranteed `apply` will throw an exception to indicate an error condition. If an exception is not thrown, evaluation may result in an arbitrary value.

The main distinction between `PartialFunction` and scala.Function1 is that the user of a `PartialFunction` may choose to do something different with input that is declared to be outside its domain. For example:

    val sample = 1 to 10
    val isEven: PartialFunction[Int, String] = {
      case x if x % 2 == 0 => x+" is even"
    }

    // the method collect can use isDefinedAt to select which members to collect
    val evenNumbers = sample collect isEven

    val isOdd: PartialFunction[Int, String] = {
      case x if x % 2 == 1 => x+" is odd"
    }

    // the method orElse allows chaining another partial function to handle
    // input outside the declared domain
    val numbers = sample map (isEven orElse isOdd)

Self Type
  PartialFunction[A, B]
Source
  PartialFunction.scala
Version

  1.0, 16/07/2003

Linear Supertypes
(A) ⇒ B, AnyRef, Any
Known Subclasses
::, AbstractBuffer, AbstractMap, AbstractMap, AbstractMap, AbstractPartialFunction, AbstractSeq, AbstractSeq, AnyRefMap, Appended, Appended, ArrayBuffer, ArraySeq, ArrayStack, Buffer, BufferProxy, Cons, DefaultMap, DefaultMap, DefaultMapModel, DoubleLinkedList, DroppedWhile, DroppedWhile, DroppedWhile, Empty, EmptyView, EmptyView, Exclusive, Filtered, Filtered, Filtered, FilteredKeys, FilteredKeys, FlatMapped, FlatMapped, Forced, Forced, HashMap, HashMap, HashMap1, HashTrieMap, ImmutableMapAdaptor, Impl, Inclusive, Inclusive, IndexedSeq, IndexedSeq, IndexedSeq, IndexedSeqView, IntMap, LinearSeq, LinearSeq, LinearSeq, LinkedHashMap, LinkedList, List, ListBuffer, ListMap, ListMap, LongMap, LongMap, Map, Map, Map, Map, Map1, Map2, Map3, Map4, MapLike, MapLike, MapLike, MapProxy, MapProxy, MapProxy, MapProxyLike, Mapped, Mapped, MappedValues, MappedValues, MultiMap, MutableList, Nil, Node, NumericRange, ObservableBuffer, ObservableMap, OpenHashMap, PagedSeq, Patched, Patched, Prepended, Prepended, Queue, Queue, QueueProxy, Range, ResizableArray, Reversed, Reversed, Reversed, Script, Seq, Seq, Seq, SeqForwarder, SeqProxy, SeqView, SeqViewLike, Sliced, Sliced, Sliced, SortedMap, SortedMap, SortedMapLike, Stack, Stack, StackProxy, Stream, StreamView, StreamViewLike, StringBuilder, SynchronizedBuffer, SynchronizedMap, SynchronizedQueue, SynchronizedStack, SystemProperties, TakenWhile, TakenWhile, TakenWhile, Transformed, Transformed, Transformed, TreeMap, TrieMap, UnrolledBuffer, Vector, WithDefault, WithDefault, WithDefault, WrappedArray, WrappedString, Zipped, Zipped, ZippedAll, ZippedAll
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Inherited

1. PartialFunction
2. Function1
3. AnyRef
4. Any

Implicitly

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

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Visibility

1. Public
2. All

### Abstract Value Members

1. #### abstract def apply(v1: A): B

   Apply the body of this function to the argument.

   Apply the body of this function to the argument.

   returns

     the result of function application.

   Definition Classes
     Function1

2. #### abstract def isDefinedAt(x: A): Boolean

   Checks if a value is contained in the function's domain.

   Checks if a value is contained in the function's domain.

   x

     the value to test

   returns

     `true`, iff `x` is in the domain of this function, `false` otherwise.

### 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 information
     This member is added by an implicit conversion from PartialFunction[A, B] to any2stringadd[PartialFunction[A, B]] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd

4. #### def ->[B](y: B): (PartialFunction[A, B], B)

   Implicit information
     This member is added by an implicit conversion from PartialFunction[A, B] to ArrowAssoc[PartialFunction[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. #### def andThen[C](k: (B) ⇒ C): PartialFunction[A, C]

   Composes this partial function with a transformation function that gets applied to results of this partial function.

   Composes this partial function with a transformation function that gets applied to results of this partial function.

   C

     the result type of the transformation function.

   k

     the transformation function

   returns

     a partial function with the same domain as this partial function, which maps arguments `x` to `k(this(x))`.

   Definition Classes
     PartialFunction → Function1

7. #### def applyOrElse[A1 <: A, B1 >: B](x: A1, default: (A1) ⇒ B1): B1

   Applies this partial function to the given argument when it is contained in the function domain.

   Applies this partial function to the given argument when it is contained in the function domain. Applies fallback function where this partial function is not defined.

   Note that expression `pf.applyOrElse(x, default)` is equivalent to

       if(pf isDefinedAt x) pf(x) else default(x)

   except that `applyOrElse` method can be implemented more efficiently. For all partial function literals the compiler generates an `applyOrElse` implementation which avoids double evaluation of pattern matchers and guards. This makes `applyOrElse` the basis for the efficient implementation for many operations and scenarios, such as:

   - combining partial functions into `orElse`/`andThen` chains does not lead to excessive `apply`/`isDefinedAt` evaluation
   - `lift` and `unlift` do not evaluate source functions twice on each invocation
   - `runWith` allows efficient imperative-style combining of partial functions with conditionally applied actions

   For non-literal partial function classes with nontrivial `isDefinedAt` method it is recommended to override `applyOrElse` with custom implementation that avoids double `isDefinedAt` evaluation. This may result in better performance and more predictable behavior w.r.t. side effects.

   x

     the function argument

   default

     the fallback function

   returns

     the result of this function or fallback function application.

   Since

     2.10

8. #### 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`.

9. #### 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[java.lang]
   Definition Classes
     AnyRef
   Annotations
     @throws( ... )
   Note

     not specified by SLS as a member of AnyRef

10. #### def compose[A](g: (A) ⇒ A): (A) ⇒ B

    Composes two instances of Function1 in a new Function1, with this function applied last.

    Composes two instances of Function1 in a new Function1, with this function applied last.

    A

      the type to which function `g` can be applied

    g

      a function A => T1

    returns

      a new function `f` such that `f(x) == apply(g(x))`

    Definition Classes
      Function1
    Annotations
      @unspecialized()

11. #### def ensuring(cond: (PartialFunction[A, B]) ⇒ Boolean, msg: ⇒ Any): PartialFunction[A, B]

    Implicit information
      This member is added by an implicit conversion from PartialFunction[A, B] to Ensuring[PartialFunction[A, B]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

12. #### def ensuring(cond: (PartialFunction[A, B]) ⇒ Boolean): PartialFunction[A, B]

    Implicit information
      This member is added by an implicit conversion from PartialFunction[A, B] to Ensuring[PartialFunction[A, B]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

13. #### def ensuring(cond: Boolean, msg: ⇒ Any): PartialFunction[A, B]

    Implicit information
      This member is added by an implicit conversion from PartialFunction[A, B] to Ensuring[PartialFunction[A, B]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

14. #### def ensuring(cond: Boolean): PartialFunction[A, B]

    Implicit information
      This member is added by an implicit conversion from PartialFunction[A, B] to Ensuring[PartialFunction[A, B]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

15. #### 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

16. #### def equals(arg0: Any): 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

17. #### 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[java.lang]
    Definition Classes
      AnyRef
    Annotations
      @throws( classOf[java.lang.Throwable] )
    Note

      not specified by SLS as a member of AnyRef

18. #### 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 information
      This member is added by an implicit conversion from PartialFunction[A, B] to StringFormat[PartialFunction[A, B]] performed by method StringFormat in scala.Predef.
    Definition Classes
      StringFormat
    Annotations
      @inline()

19. #### final def getClass(): Class[_]

    A representation that corresponds to the dynamic class of the receiver object.

    A representation that corresponds to the dynamic class of the receiver object.

    The nature of the representation is platform dependent.

    returns

      a representation that corresponds to the dynamic class of the receiver object.

    Definition Classes
      AnyRef → Any
    Note

      not specified by SLS as a member of AnyRef

20. #### 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

21. #### 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

22. #### def lift: (A) ⇒ Option[B]

    Turns this partial function into a plain function returning an `Option` result.

    Turns this partial function into a plain function returning an `Option` result.

    returns

      a function that takes an argument `x` to `Some(this(x))` if `this` is defined for `x`, and to `None` otherwise.

    See also

      Function.unlift

23. #### 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

24. #### 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
    Note

      not specified by SLS as a member of AnyRef

25. #### 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
    Note

      not specified by SLS as a member of AnyRef

26. #### def orElse[A1 <: A, B1 >: B](that: PartialFunction[A1, B1]): PartialFunction[A1, B1]

    Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.

    Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.

    A1

      the argument type of the fallback function

    B1

      the result type of the fallback function

    that

      the fallback function

    returns

      a partial function which has as domain the union of the domains of this partial function and `that`. The resulting partial function takes `x` to `this(x)` where `this` is defined, and to `that(x)` where it is not.

27. #### def runWith[U](action: (B) ⇒ U): (A) ⇒ Boolean

    Composes this partial function with an action function which gets applied to results of this partial function.

    Composes this partial function with an action function which gets applied to results of this partial function. The action function is invoked only for its side effects; its result is ignored.

    Note that expression `pf.runWith(action)(x)` is equivalent to

        if(pf isDefinedAt x) { action(pf(x)); true } else false

    except that `runWith` is implemented via `applyOrElse` and thus potentially more efficient. Using `runWith` avoids double evaluation of pattern matchers and guards for partial function literals.

    action

      the action function

    returns

      a function which maps arguments `x` to `isDefinedAt(x)`. The resulting function runs `action(this(x))` where `this` is defined.

    Since

      2.10

    See also

      `applyOrElse`.

28. #### final def synchronized[T0](arg0: ⇒ T0): T0

    Definition Classes
      AnyRef

29. #### 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
      Function1 → AnyRef → Any

30. #### final def wait(): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

31. #### final def wait(arg0: Long, arg1: Int): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

32. #### final def wait(arg0: Long): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

33. #### def →[B](y: B): (PartialFunction[A, B], B)

    Implicit information
      This member is added by an implicit conversion from PartialFunction[A, B] to ArrowAssoc[PartialFunction[A, B]] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
      ArrowAssoc

### Inherited from (A) ⇒ B

### Inherited from AnyRef

### Inherited from Any

### Inherited by implicit conversion any2stringadd from PartialFunction[A, B] to any2stringadd[PartialFunction[A, B]]

### Inherited by implicit conversion StringFormat from PartialFunction[A, B] to StringFormat[PartialFunction[A, B]]

### Inherited by implicit conversion Ensuring from PartialFunction[A, B] to Ensuring[PartialFunction[A, B]]

### Inherited by implicit conversion ArrowAssoc from PartialFunction[A, B] to ArrowAssoc[PartialFunction[A, B]]

### Ungrouped