Package io.vavr

Interface Function1<T1,R>

Type Parameters:

T1 - argument 1 of the function

R - return type of the function

All Superinterfaces:

java.util.function.Function<T1,R>, java.io.Serializable

All Known Subinterfaces:

API.Match.Case<T,R>, API.Match.Pattern<T,R>, IndexedSeq<T>, LinearSeq<T>, Map<K,V>, Multimap<K,V>, PartialFunction<T,R>, Seq<T>, Set<T>, SortedMap<K,V>, SortedMultimap<K,V>, SortedSet<T>

All Known Implementing Classes:

API.Match.Case0, API.Match.Case1, API.Match.Case2, API.Match.Case3, API.Match.Case4, API.Match.Case5, API.Match.Case6, API.Match.Case7, API.Match.Case8, API.Match.Pattern0, API.Match.Pattern1, API.Match.Pattern2, API.Match.Pattern3, API.Match.Pattern4, API.Match.Pattern5, API.Match.Pattern6, API.Match.Pattern7, API.Match.Pattern8, Array, BitSet, CharSeq, HashMap, HashMultimap, HashSet, LinkedHashMap, LinkedHashMultimap, LinkedHashSet, List, List.Cons, List.Nil, Queue, Stream, Stream.Cons, Stream.Empty, TreeMap, TreeMultimap, TreeSet, Vector

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public interface Function1<T1,R>
extends java.io.Serializable, java.util.function.Function<T1,R>

Represents a function with one argument.

Field Summary

Fields

Modifier and Type	Field	Description
static long	serialVersionUID	The serial version uid.

Method Summary

Modifier and Type	Method	Description
default <V> Function1<T1,V>	andThen(java.util.function.Function<? super R,? extends V> after)	Returns a composed function that first applies this Function1 to the given argument and then applies Function after to the result.
R	apply(T1 t1)	Applies this function to one argument and returns the result.
default int	arity()	Returns the number of function arguments.
default <V> Function1<V,R>	compose(java.util.function.Function<? super V,? extends T1> before)	Returns a composed function that first applies the Function before the given argument and then applies this Function1 to the result.
static <T1,R> Function1<T1,R>	constant(R value)	Returns a function that always returns the constant value that you give in parameter.
default Function1<T1,R>	curried()	Returns a curried version of this function.
static <T> Function1<T,T>	identity()	Returns the identity Function1, i.e.
default boolean	isMemoized()	Checks if this function is memoizing (= caching) computed values.
static <T1,R> Function1<T1,Option<R>>	lift(java.util.function.Function<? super T1,? extends R> partialFunction)	Lifts the given partialFunction into a total function that returns an Option result.
static <T1,R> Function1<T1,Try<R>>	liftTry(java.util.function.Function<? super T1,? extends R> partialFunction)	Lifts the given partialFunction into a total function that returns an Try result.
default Function1<T1,R>	memoized()	Returns a memoizing version of this function, which computes the return value for given arguments only one time.
static <T1,R> Function1<T1,R>	narrow(Function1<? super T1,? extends R> f)	Narrows the given Function1<? super T1, ? extends R> to Function1<T1, R>
static <T1,R> Function1<T1,R>	of(Function1<T1,R> methodReference)	Creates a Function1 based on method reference lambda expression Examples (w.l.o.g.
default PartialFunction<T1,R>	partial(java.util.function.Predicate<? super T1> isDefinedAt)	Converts this Function1 to a PartialFunction by adding an isDefinedAt condition.
default Function1<T1,R>	reversed()	Returns a reversed version of this function.
default Function1<Tuple1<T1>,R>	tupled()	Returns a tupled version of this function.

Field Detail

serialVersionUID

static final long serialVersionUID

The serial version uid.

See Also:

Constant Field Values

Method Detail

constant

static <T1,R> Function1<T1,R> constant(R value)

Returns a function that always returns the constant value that you give in parameter.

Type Parameters:

T1 - generic parameter type 1 of the resulting function

R - the result type

Parameters:

value - the value to be returned

Returns:

a function always returning the given value

of

static <T1,R> Function1<T1,R> of(Function1<T1,R> methodReference)

Creates a Function1 based on

• method reference
• lambda expression

Examples (w.l.o.g. referring to Function1):

// using a lambda expression
 Function1<Integer, Integer> add1 = Function1.of(i -> i + 1);

 // using a method reference (, e.g. Integer method(Integer i) { return i + 1; })
 Function1<Integer, Integer> add2 = Function1.of(this::method);

 // using a lambda reference
 Function1<Integer, Integer> add3 = Function1.of(add1::apply);
 

Caution: Reflection loses type information of lambda references.

// type of a lambda expression
 Type<?, ?> type1 = add1.getType(); // (Integer) -> Integer

 // type of a method reference
 Type<?, ?> type2 = add2.getType(); // (Integer) -> Integer

 // type of a lambda reference
 Type<?, ?> type3 = add3.getType(); // (Object) -> Object
 

Type Parameters:

R - return type

T1 - 1st argument

Parameters:

methodReference - (typically) a method reference, e.g. Type::method

Returns:

a Function1

lift

static <T1,R> Function1<T1,Option<R>> lift(java.util.function.Function<? super T1,? extends R> partialFunction)

Lifts the given partialFunction into a total function that returns an Option result.

Type Parameters:

R - return type

T1 - 1st argument

Parameters:

partialFunction - a function that is not defined for all values of the domain (e.g. by throwing)

Returns:

a function that applies arguments to the given partialFunction and returns Some(result) if the function is defined for the given arguments, and None otherwise.

liftTry

static <T1,R> Function1<T1,Try<R>> liftTry(java.util.function.Function<? super T1,? extends R> partialFunction)

Lifts the given partialFunction into a total function that returns an Try result.

Type Parameters:

R - return type

T1 - 1st argument

Parameters:

partialFunction - a function that is not defined for all values of the domain (e.g. by throwing)

Returns:

a function that applies arguments to the given partialFunction and returns Success(result) if the function is defined for the given arguments, and Failure(throwable) otherwise.

narrow

static <T1,R> Function1<T1,R> narrow(Function1<? super T1,? extends R> f)

Narrows the given Function1<? super T1, ? extends R> to Function1<T1, R>

Type Parameters:

R - return type

T1 - 1st argument

Parameters:

f - A Function1

Returns:

the given f instance as narrowed type Function1<T1, R>

identity

static <T> Function1<T,T> identity()

Returns the identity Function1, i.e. the function that returns its input.

Type Parameters:

T - argument type (and return type) of the identity function

Returns:

the identity Function1

apply

R apply(T1 t1)

Applies this function to one argument and returns the result.

Specified by:

apply in interface java.util.function.Function<T1,R>

Parameters:

t1 - argument 1

Returns:

the result of function application

arity

default int arity()

Returns the number of function arguments.

Returns:

an int value >= 0

See Also:

Arity

curried

default Function1<T1,R> curried()

Returns a curried version of this function.

Returns:

a curried function equivalent to this.

tupled

default Function1<Tuple1<T1>,R> tupled()

Returns a tupled version of this function.

Returns:

a tupled function equivalent to this.

reversed

default Function1<T1,R> reversed()

Returns a reversed version of this function. This may be useful in a recursive context.

Returns:

a reversed function equivalent to this.

memoized

default Function1<T1,R> memoized()

Returns a memoizing version of this function, which computes the return value for given arguments only one time. On subsequent calls given the same arguments the memoized value is returned.

Please note that memoizing functions do not permit null as single argument or return value.

Returns:

a memoizing function equivalent to this.

isMemoized

default boolean isMemoized()

Checks if this function is memoizing (= caching) computed values.

Returns:

true, if this function is memoizing, false otherwise

partial

default PartialFunction<T1,R> partial(java.util.function.Predicate<? super T1> isDefinedAt)

Converts this Function1 to a PartialFunction by adding an isDefinedAt condition.

Parameters:

isDefinedAt - a predicate that states if an element is in the domain of the returned PartialFunction.

Returns:

a new PartialFunction that has the same behavior like this function but is defined only for those elements that make it through the given Predicate

Throws:

java.lang.NullPointerException - if isDefinedAt is null

andThen

default <V> Function1<T1,V> andThen(java.util.function.Function<? super R,? extends V> after)

Returns a composed function that first applies this Function1 to the given argument and then applies Function after to the result.

Specified by:

andThen in interface java.util.function.Function<T1,R>

Type Parameters:

V - return type of after

Parameters:

after - the function applied after this

Returns:

a function composed of this and after

Throws:

java.lang.NullPointerException - if after is null

compose

default <V> Function1<V,R> compose(java.util.function.Function<? super V,? extends T1> before)

Returns a composed function that first applies the Function before the given argument and then applies this Function1 to the result.

Specified by:

compose in interface java.util.function.Function<T1,R>

Type Parameters:

V - argument type of before

Parameters:

before - the function applied before this

Returns:

a function composed of before and this

Throws:

java.lang.NullPointerException - if before is null