Set.java

/* ____  ______________  ________________________  __________
 * \   \/   /      \   \/   /   __/   /      \   \/   /      \
 *  \______/___/\___\______/___/_____/___/\___\______/___/\___\
 *
 * Copyright 2021 Vavr, https://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.collection;

import io.vavr.*;
import io.vavr.control.Option;

import java.io.Serializable;
import java.util.Comparator;
import java.util.function.*;

/**
 * An immutable {@code Set} interface.
 * <p>
 * CAUTION: The Vavr {@code Set} implementations generally support {@code null} elements. However {@code SortedSet}
 * implementations require an element {@code Comparator}, which may not support {@code null} elements.
 * <p>
 * Examples:
 *
 * <pre>{@code Set<?> addNull(Set<?> set) {
 *
 *     // CAUTION: Do not expect a Set to accept null values in general!
 *     return set.add(null);
 *
 * }
 *
 * void test() {
 *
 *     // ok
 *     addNull(HashSet.of(1));
 *
 *     // ok
 *     addNull(TreeSet.of(nullsFirst(naturalOrder()), 1));
 *
 *     // ok
 *     addNull(TreeSet.empty());
 *
 *     // throws NPE!
 *     addNull(TreeSet.of(1));
 *
 * }}</pre>
 *
 * <p>
 * Basic operations:
 *
 * <ul>
 * <li>{@link #add(Object)}</li>
 * <li>{@link #addAll(Iterable)}</li>
 * <li>{@link #diff(Set)}</li>
 * <li>{@link #intersect(Set)}</li>
 * <li>{@link #remove(Object)}</li>
 * <li>{@link #removeAll(Iterable)}</li>
 * <li>{@link #union(Set)}</li>
 * </ul>
 *
 * Conversion:
 *
 * <ul>
 * <li>{@link #toJavaSet()}</li>
 * </ul>
 *
 * @param <T> Component type
 */
@SuppressWarnings("deprecation")
public interface Set<T> extends Traversable<T>, Serializable {

    long serialVersionUID = 1L;

    /**
     * Narrows a widened {@code Set<? extends T>} to {@code Set<T>}
     * by performing a type-safe cast. This is eligible because immutable/read-only
     * collections are covariant.
     *
     * @param set A {@code Set}.
     * @param <T> Component type of the {@code Set}.
     * @return the given {@code set} instance as narrowed type {@code Set<T>}.
     */
    @SuppressWarnings("unchecked")
    static <T> Set<T> narrow(Set<? extends T> set) {
        return (Set<T>) set;
    }

    /**
     * Add the given element to this set, if it is not already contained.
     *
     * @param element The element to be added.
     * @return A new set containing all elements of this set and also {@code element}.
     */
    Set<T> add(T element);

    /**
     * Adds all of the given elements to this set, if not already contained.
     *
     * @param elements The elements to be added.
     * @return A new set containing all elements of this set and the given {@code elements}, if not already contained.
     */
    Set<T> addAll(Iterable<? extends T> elements);

    /**
     * Calculates the difference between this set and another set.
     * <p>
     * See also {@link #removeAll(Iterable)}.
     *
     * @param that Elements to be removed from this set.
     * @return A new Set containing all elements of this set which are not located in {@code that} set.
     */
    Set<T> diff(Set<? extends T> that);

    /**
     * Computes the intersection between this set and another set.
     * <p>
     * See also {@link #retainAll(Iterable)}.
     *
     * @param that the set to intersect with.
     * @return A new Set consisting of all elements that are both in this set and in the given set {@code that}.
     */
    Set<T> intersect(Set<? extends T> that);

    /**
     * Removes a specific element from this set, if present.
     *
     * @param element The element to be removed from this set.
     * @return A new set consisting of the elements of this set, without the given {@code element}.
     */
    Set<T> remove(T element);

    /**
     * Removes all of the given elements from this set, if present.
     *
     * @param elements The elements to be removed from this set.
     * @return A new set consisting of the elements of this set, without the given {@code elements}.
     */
    Set<T> removeAll(Iterable<? extends T> elements);

    /**
     * Converts this Vavr {@code Set} to a {@code java.util.Set} while preserving characteristics
     * like insertion order ({@code LinkedHashSet}) and sort order ({@code SortedSet}).
     *
     * @return a new {@code java.util.Set} instance
     */
    @Override
    java.util.Set<T> toJavaSet();

    /**
     * Adds all of the elements of {@code that} set to this set, if not already present.
     * <p>
     * See also {@link #addAll(Iterable)}.
     *
     * @param that The set to form the union with.
     * @return A new set that contains all distinct elements of this and {@code that} set.
     */
    Set<T> union(Set<? extends T> that);

    // -- Adjusted return types of Traversable methods

    @Override
    <R> Set<R> collect(PartialFunction<? super T, ? extends R> partialFunction);

    @Override
    boolean contains(T element);

    @Override
    Set<T> distinct();

    @Override
    Set<T> distinctBy(Comparator<? super T> comparator);

    @Override
    <U> Set<T> distinctBy(Function<? super T, ? extends U> keyExtractor);

    @Override
    Set<T> drop(int n);

    @Override
    Set<T> dropRight(int n);

    @Override
    Set<T> dropUntil(Predicate<? super T> predicate);

    @Override
    Set<T> dropWhile(Predicate<? super T> predicate);

    @Override
    Set<T> filter(Predicate<? super T> predicate);

    @Override
    Set<T> filterNot(Predicate<? super T> predicate);

    @Override
    <U> Set<U> flatMap(Function<? super T, ? extends Iterable<? extends U>> mapper);

    @Override
    <C> Map<C, ? extends Set<T>> groupBy(Function<? super T, ? extends C> classifier);

    @Override
    Iterator<? extends Set<T>> grouped(int size);

    @Override
    Set<T> init();

    @Override
    Option<? extends Set<T>> initOption();

    @Override
    default boolean isDistinct() {
        return true;
    }

    @Override
    Iterator<T> iterator();

    @Override
    int length();

    @Override
    <U> Set<U> map(Function<? super T, ? extends U> mapper);

    @Override
    Set<T> orElse(Iterable<? extends T> other);

    @Override
    Set<T> orElse(Supplier<? extends Iterable<? extends T>> supplier);

    @Override
    Tuple2<? extends Set<T>, ? extends Set<T>> partition(Predicate<? super T> predicate);

    @Override
    Set<T> peek(Consumer<? super T> action);

    @Override
    Set<T> tapEach(Consumer<? super T> action);
    
    @Override
    Set<T> replace(T currentElement, T newElement);

    @Override
    Set<T> replaceAll(T currentElement, T newElement);

    @Override
    Set<T> retainAll(Iterable<? extends T> elements);

    @Override
    Set<T> scan(T zero, BiFunction<? super T, ? super T, ? extends T> operation);

    @Override
    <U> Set<U> scanLeft(U zero, BiFunction<? super U, ? super T, ? extends U> operation);

    @Override
    <U> Set<U> scanRight(U zero, BiFunction<? super T, ? super U, ? extends U> operation);

    @Override
    Iterator<? extends Set<T>> slideBy(Function<? super T, ?> classifier);

    @Override
    Iterator<? extends Set<T>> sliding(int size);

    @Override
    Iterator<? extends Set<T>> sliding(int size, int step);

    @Override
    Tuple2<? extends Set<T>, ? extends Set<T>> span(Predicate<? super T> predicate);

    @Override
    Set<T> tail();

    @Override
    Option<? extends Set<T>> tailOption();

    @Override
    Set<T> take(int n);

    @Override
    Set<T> takeRight(int n);

    @Override
    Set<T> takeUntil(Predicate<? super T> predicate);

    @Override
    Set<T> takeWhile(Predicate<? super T> predicate);

    @Override
    <T1, T2> Tuple2<? extends Set<T1>, ? extends Set<T2>> unzip(Function<? super T, Tuple2<? extends T1, ? extends T2>> unzipper);

    @Override
    <T1, T2, T3> Tuple3<? extends Set<T1>, ? extends Set<T2>, ? extends Set<T3>> unzip3(Function<? super T, Tuple3<? extends T1, ? extends T2, ? extends T3>> unzipper);

    @Override
    <U> Set<Tuple2<T, U>> zip(Iterable<? extends U> that);

    @Override
    <U, R> Set<R> zipWith(Iterable<? extends U> that, BiFunction<? super T, ? super U, ? extends R> mapper);

    @Override
    <U> Set<Tuple2<T, U>> zipAll(Iterable<? extends U> that, T thisElem, U thatElem);

    @Override
    Set<Tuple2<T, Integer>> zipWithIndex();

    @Override
    <U> Set<U> zipWithIndex(BiFunction<? super T, ? super Integer, ? extends U> mapper);
}