io.vavr.Function1 Maven / Gradle / Ivy
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/* __ __ __ __ __ ___
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* \ \/ / /\ \ \/ / /
* \____/__/ \__\____/__/
*
* Copyright 2014-2019 Vavr, http://vavr.io
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package io.vavr;
/*-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-*\
G E N E R A T O R C R A F T E D
\*-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-*/
import io.vavr.control.Option;
import io.vavr.control.Try;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;
import java.util.function.Function;
import java.util.function.Predicate;
/**
* Represents a function with one argument.
*
* @param argument 1 of the function
* @param return type of the function
* @author Daniel Dietrich
*/
@FunctionalInterface
public interface Function1 extends Serializable, Function {
/**
* The serial version uid.
*/
long serialVersionUID = 1L;
/**
* Returns a function that always returns the constant
* value that you give in parameter.
*
* @param generic parameter type 1 of the resulting function
* @param the result type
* @param value the value to be returned
* @return a function always returning the given value
*/
static Function1 constant(R value) {
return (t1) -> value;
}
/**
* Creates a {@code Function1} based on
*
*
* 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
*
*
* @param methodReference (typically) a method reference, e.g. {@code Type::method}
* @param return type
* @param 1st argument
* @return a {@code Function1}
*/
static Function1 of(Function1 methodReference) {
return methodReference;
}
/**
* Lifts the given {@code partialFunction} into a total function that returns an {@code Option} result.
*
* @param partialFunction a function that is not defined for all values of the domain (e.g. by throwing)
* @param return type
* @param 1st argument
* @return a function that applies arguments to the given {@code partialFunction} and returns {@code Some(result)}
* if the function is defined for the given arguments, and {@code None} otherwise.
*/
@SuppressWarnings("RedundantTypeArguments")
static Function1> lift(Function partialFunction) {
return t1 -> Try.of(() -> partialFunction.apply(t1)).toOption();
}
/**
* Lifts the given {@code partialFunction} into a total function that returns an {@code Try} result.
*
* @param partialFunction a function that is not defined for all values of the domain (e.g. by throwing)
* @param return type
* @param 1st argument
* @return a function that applies arguments to the given {@code partialFunction} and returns {@code Success(result)}
* if the function is defined for the given arguments, and {@code Failure(throwable)} otherwise.
*/
static Function1> liftTry(Function partialFunction) {
return t1 -> Try.of(() -> partialFunction.apply(t1));
}
/**
* Narrows the given {@code Function1} to {@code Function1}
*
* @param f A {@code Function1}
* @param return type
* @param 1st argument
* @return the given {@code f} instance as narrowed type {@code Function1}
*/
@SuppressWarnings("unchecked")
static Function1 narrow(Function1 f) {
return (Function1) f;
}
/**
* Returns the identity Function1, i.e. the function that returns its input.
*
* @param argument type (and return type) of the identity function
* @return the identity Function1
*/
static Function1 identity() {
return t -> t;
}
/**
* Applies this function to one argument and returns the result.
*
* @param t1 argument 1
* @return the result of function application
*
*/
R apply(T1 t1);
/**
* Returns the number of function arguments.
* @return an int value >= 0
* @see Arity
*/
default int arity() {
return 1;
}
/**
* Returns a curried version of this function.
*
* @return a curried function equivalent to this.
*/
default Function1 curried() {
return this;
}
/**
* Returns a tupled version of this function.
*
* @return a tupled function equivalent to this.
*/
default Function1, R> tupled() {
return t -> apply(t._1);
}
/**
* Returns a reversed version of this function. This may be useful in a recursive context.
*
* @return a reversed function equivalent to this.
*/
default Function1 reversed() {
return this;
}
/**
* 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 {@code null} as single argument or return value.
*
* @return a memoizing function equivalent to this.
*/
default Function1 memoized() {
if (isMemoized()) {
return this;
} else {
final Map cache = new HashMap<>();
return (Function1 & Memoized) (t1) -> {
synchronized (cache) {
if (cache.containsKey(t1)) {
return cache.get(t1);
} else {
final R value = apply(t1);
cache.put(t1, value);
return value;
}
}
};
}
}
/**
* Checks if this function is memoizing (= caching) computed values.
*
* @return true, if this function is memoizing, false otherwise
*/
default boolean isMemoized() {
return this instanceof Memoized;
}
/**
* Converts this {@code Function1} to a {@link PartialFunction} by adding an {@code isDefinedAt} condition.
*
* @param isDefinedAt a predicate that states if an element is in the domain of the returned {@code PartialFunction}.
* @return a new {@code PartialFunction} that has the same behavior like this function but is defined only for those elements that make it through the given {@code Predicate}
* @throws NullPointerException if {@code isDefinedAt} is null
*/
default PartialFunction partial(Predicate isDefinedAt) {
Objects.requireNonNull(isDefinedAt, "isDefinedAt is null");
final Function1 self = this;
return new PartialFunction() {
private static final long serialVersionUID = 1L;
@Override
public boolean isDefinedAt(T1 t1) {
return isDefinedAt.test(t1);
}
@Override
public R apply(T1 t1) {
return self.apply(t1);
}
};
}
/**
* Returns a composed function that first applies this Function1 to the given argument and then applies
* {@linkplain Function} {@code after} to the result.
*
* @param return type of after
* @param after the function applied after this
* @return a function composed of this and after
* @throws NullPointerException if after is null
*/
default Function1 andThen(Function after) {
Objects.requireNonNull(after, "after is null");
return (t1) -> after.apply(apply(t1));
}
/**
* Returns a composed function that first applies the {@linkplain Function} {@code before} the
* given argument and then applies this Function1 to the result.
*
* @param argument type of before
* @param before the function applied before this
* @return a function composed of before and this
* @throws NullPointerException if before is null
*/
default Function1 compose(Function before) {
Objects.requireNonNull(before, "before is null");
return v -> apply(before.apply(v));
}
}