Apply the body of this function to the argument.
the result of function application.
Checks if a value is contained in the function's domain.
the value to test
true, iff x is in the domain of this function, false otherwise.
Test two objects for inequality.
true if !(this == that), false otherwise.
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.
a hash value consistent with ==
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
true if the receiver object is equivalent to the argument; false otherwise.
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.
the result type of the transformation function.
the transformation function
a partial function with the domain of this partial function narrowed by other partial function, which maps arguments x to k(this(x)).
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).
the result type of the transformation function.
the transformation function
a partial function with the domain of this partial function, possibly narrowed by the specified function, which maps arguments x to k(this(x)).
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:
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.
the function argument
the fallback function
the result of this function or fallback function application.
2.10
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.
the receiver object.
ClassCastException if the receiver object is not an instance of the erasure of type T0.
Create a copy of the receiver object.
The default implementation of the clone method is platform dependent.
a copy of the receiver object.
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.
the parameter type of the transformation function.
the transformation function
a partial function with the domain of other partial function narrowed by this partial function, which maps arguments x to this(k(x)).
Composes two instances of Function1 in a new Function1, with this function applied last.
the type to which function g can be applied
a function A => T1
a new function f such that f(x) == apply(g(x))
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
}
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:
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).
true if the argument is a reference to the receiver object; false otherwise.
The equality method for reference types. Default implementation delegates to eq.
See also equals in scala.Any.
true if the receiver object is equivalent to the argument; false otherwise.
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.
Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).
Returns the runtime class representation of the object.
a class object corresponding to the runtime type of the receiver.
The hashCode method for reference types. See hashCode in scala.Any.
the hash code value for this object.
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.
true if the receiver object is an instance of erasure of type T0; false otherwise.
Turns this partial function into a plain function returning an Option result.
a function that takes an argument x to Some(this(x)) if this is defined for x, and to None otherwise.
Function.unlift
Equivalent to !(this eq that).
true if the argument is not a reference to the receiver object; false otherwise.
Wakes up a single thread that is waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
Wakes up all threads that are waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.
the argument type of the fallback function
the result type of the fallback function
the fallback function
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.
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.
the action function
a function which maps arguments x to isDefinedAt(x). The resulting function runs action(this(x)) where this is defined.
2.10
applyOrElse.
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.
a String representation of the object.
Converts an optional function to a partial function.
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")
}
© 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 functionisDefinedAtallows to test dynamically if a value is in the domain of the function.Even if
isDefinedAtreturns true for ana: A, callingapply(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
isDefinedAtbefore callingapply, because ifisDefinedAtis false, it is not guaranteedapplywill 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
PartialFunctionand scala.Function1 is that the user of aPartialFunctionmay 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)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 |