Trait scala.PartialFunction
Companion object PartialFunction
trait PartialFunction[-A, +B] extends (A) => B
Abstract Value Members
abstract def apply(v1: A): B
Apply the body of this function to the argument.
- returns
the result of function application.
- Definition Classes
- Function1
abstract def isDefinedAt(x: A): Boolean
Checks if a value is contained in the function's domain.
- x
the value to test
- returns
true
, iffx
is in the domain of this function,false
otherwise.
Concrete Value Members
final def !=(arg0: Any): Boolean
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 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
def +(other: String): String
- Implicit
- This member is added by an implicit conversion from PartialFunction[A, B] toany2stringadd[PartialFunction[A, B]] performed by method any2stringadd in scala.Predef.
- Definition Classes
- any2stringadd
def ->[B](y: B): (PartialFunction[A, B], B)
- Implicit
- This member is added by an implicit conversion from PartialFunction[A, B] toArrowAssoc[PartialFunction[A, B]] performed by method ArrowAssoc in scala.Predef.This conversion will take place only if B is a subclass of Option[Nothing] (B <: Option[Nothing]).
- Definition Classes
- ArrowAssoc
- Annotations
- @inline()
final def ==(arg0: Any): Boolean
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
def andThen[C](k: PartialFunction[B, C]): PartialFunction[A, C]
Composes this partial function with another partial function that gets applied to results of this partial function.
Note that calling isDefinedAt on the resulting partial function may apply the first partial function and execute its side effect. It is highly recommended to call applyOrElse instead of isDefinedAt / apply for efficiency.
- C
the result type of the transformation function.
- k
the transformation function
- returns
a partial function with the domain of this partial function narrowed by other partial function, which maps arguments
x
tok(this(x))
.
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.
If the runtime type of the function is a PartialFunction
then the other andThen
method is used (note its cautions).
- C
the result type of the transformation function.
- k
the transformation function
- returns
a partial function with the domain of this partial function, possibly narrowed by the specified function, which maps arguments
x
tok(this(x))
.
- Definition Classes
- PartialFunction → Function1
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 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
final def asInstanceOf[T0]: 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 typeT0
.
def clone(): AnyRef
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 compose[R](k: PartialFunction[R, A]): PartialFunction[R, B]
Composes another partial function k
with this partial function so that this partial function gets applied to results of k
.
Note that calling isDefinedAt on the resulting partial function may apply the first partial function and execute its side effect. It is highly recommended to call applyOrElse instead of isDefinedAt / apply for efficiency.
- R
the parameter type of the transformation function.
- k
the transformation function
- returns
a partial function with the domain of other partial function narrowed by this partial function, which maps arguments
x
tothis(k(x))
.
def compose[A](g: (A) => A): (A) => B
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 thatf(x) == apply(g(x))
- Definition Classes
- Function1
- Annotations
- @unspecialized()
def elementWise: ElementWiseExtractor[A, B]
Returns an extractor object with a unapplySeq
method, which extracts each element of a sequence data.
val firstChar: String => Option[Char] = _.headOption Seq("foo", "bar", "baz") match { case firstChar.unlift.elementWise(c0, c1, c2) => println(s"$c0, $c1, $c2") // Output: f, b, b }
def ensuring(cond: (PartialFunction[A, B]) => Boolean, msg: => Any): PartialFunction[A, B]
- Implicit
- This member is added by an implicit conversion from PartialFunction[A, B] toEnsuring[PartialFunction[A, B]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
def ensuring(cond: (PartialFunction[A, B]) => Boolean): PartialFunction[A, B]
- Implicit
- This member is added by an implicit conversion from PartialFunction[A, B] toEnsuring[PartialFunction[A, B]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
def ensuring(cond: Boolean, msg: => Any): PartialFunction[A, B]
- Implicit
- This member is added by an implicit conversion from PartialFunction[A, B] toEnsuring[PartialFunction[A, B]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
def ensuring(cond: Boolean): PartialFunction[A, B]
- Implicit
- This member is added by an implicit conversion from PartialFunction[A, B] toEnsuring[PartialFunction[A, B]] 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
).
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
def equals(arg0: AnyRef): Boolean
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
def finalize(): Unit
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.
def formatted(fmtstr: String): 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 PartialFunction[A, B] toStringFormat[PartialFunction[A, B]] performed by method StringFormat in scala.Predef.
- Definition Classes
- StringFormat
- Annotations
- @inline()
final def getClass(): Class[_ <: AnyRef]
Returns the runtime class representation of the object.
- returns
a class object corresponding to the runtime type of the receiver.
def hashCode(): Int
The hashCode method for reference types. See hashCode in scala.Any.
- returns
the hash code value for this object.
final def isInstanceOf[T0]: Boolean
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 typeT0
;false
otherwise.
- Definition Classes
- Any
def lift: (A) => Option[B]
Turns this partial function into a plain function returning an Option
result.
- returns
a function that takes an argument
x
toSome(this(x))
ifthis
is defined forx
, and toNone
otherwise.
- See also
Function.unlift
final def ne(arg0: AnyRef): Boolean
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.
- 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.
- Definition Classes
- AnyRef
- Annotations
- @native()
- Note
not specified by SLS as a member of AnyRef
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.
- 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 takesx
tothis(x)
wherethis
is defined, and tothat(x)
where it is not.
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. 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
toisDefinedAt(x)
. The resulting function runsaction(this(x))
wherethis
is defined.
- Since
2.10
- See also
applyOrElse
.
final def synchronized[T0](arg0: => T0): T0
- Definition Classes
- AnyRef
def toString(): String
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.
def unapply(a: A): Option[B]
def unlift: PartialFunction[A, B]
Converts an optional function to a partial function.
- Implicit
- This member is added by an implicit conversion from PartialFunction[A, B] toUnliftOps[A, B] performed by method UnliftOps in scala.Function1.This conversion will take place only if B is a subclass of Option[B] (B <: Option[B]).
- Definition Classes
- UnliftOps
Unlike Function.unlift, this UnliftOps.unlift method can be used in extractors.
val of: Int => Option[String] = { i => if (i == 2) { Some("matched by an optional function") } else { None } } util.Random.nextInt(4) match { case of.unlift(m) => // Convert an optional function to a pattern println(m) case _ => println("Not matched") }
final def wait(): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
final def wait(arg0: Long, arg1: Int): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
final def wait(arg0: Long): Unit
© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.13.0/scala/PartialFunction.html
A partial function of type
PartialFunction[A, B]
is a unary function where the domain does not necessarily include all values of typeA
. The functionisDefinedAt
allows to test dynamically if a value is in the domain of the function.Even if
isDefinedAt
returns true for ana: A
, callingapply(a)
may still throw an exception, so the following code is legal:It is the responsibility of the caller to call
isDefinedAt
before callingapply
, because ifisDefinedAt
is false, it is not guaranteedapply
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 aPartialFunction
may choose to do something different with input that is declared to be outside its domain. For example:1.0
Optional Functions, PartialFunctions and extractor objects can be converted to each other as shown in the following table. | How to convert ... | to a PartialFunction | to an optional Function | to an extractor | | :---: | --- | --- | --- | | from a PartialFunction | Predef.identity | lift | Predef.identity | | from optional Function | Function.UnliftOps#unlift or Function.unlift | Predef.identity | Function.UnliftOps#unlift | | from an extractor |
{ case extractor(x) => x }
|extractor.unapply _
| Predef.identity |