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/*******************************************************************************
* Copyright (c) 2010-2019, Gabor Bergmann, IncQuery Labs Ltd.
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0 which is available at
* http://www.eclipse.org/legal/epl-v20.html.
*
* SPDX-License-Identifier: EPL-2.0
*
* Contributors:
* Gabor Bergmann - initial API and implementation
*******************************************************************************/
package tools.refinery.viatra.runtime.matchers.util;
import java.util.ArrayList;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;
/**
* This class was motivated by the similar Sets class from Guava to provide simple set manipulation
* functionality. However, as starting with version 2.3 the runtime of VIATRA Query should not depend on Guava,
* not even internally, the relevant subset of Sets methods will be reimplemented here.
*
* <p> The current approach is to delegate to Eclipse Collections wherever possible.
* Such glue methods are useful so that downstream clients can avoid directly depending on Eclipse Collections.
*
* <p> Without an equivalent from Eclipse Collections, {@link #cartesianProduct(List)} is implemented here from scratch.
*
* @author Gabor Bergmann
* @since 2.3
*/
public final class Sets {
/**
* @since 2.4
*/
public static <A> Set<A> newSet(Iterable<A> elements) {
return org.eclipse.collections.impl.factory.Sets.mutable.ofAll(elements);
}
public static <A> Set<A> intersection(Set<A> left, Set<A> right) {
return org.eclipse.collections.impl.factory.Sets.intersect(left, right);
}
public static <A> Set<A> difference(Set<A> left, Set<A> right) {
return org.eclipse.collections.impl.factory.Sets.difference(left, right);
}
public static <A> Set<A> union(Set<A> left, Set<A> right) {
return org.eclipse.collections.impl.factory.Sets.union(left, right);
}
public static <A> Set<? extends Set<A>> powerSet(Set<A> set) {
return org.eclipse.collections.impl.factory.Sets.powerSet(set);
}
public static <A> Set<List<A>> cartesianProduct(List<? extends Set<? extends A>> setsList) {
class Suffix { // simple immutable linked list
private A head;
private Suffix next;
public Suffix(A head, Suffix next) {
super();
this.head = head;
this.next = next;
}
public List<A> toList() {
ArrayList<A> result = new ArrayList<>();
for (Suffix cursor = this; cursor!=null; cursor = cursor.next)
result.add(cursor.head);
return result;
}
}
// build result lists from end to start, in the form of suffixes
Stream<Suffix> suffixes = Stream.of((Suffix) null /* empty suffix*/);
for (int i = setsList.size()-1; i>=0; --i) { // iterate sets in reverse order
Set<? extends A> set = setsList.get(i);
suffixes = suffixes.flatMap(suffix -> set.stream().map(newElement -> new Suffix(newElement, suffix)));
}
return suffixes.map(Suffix::toList).collect(Collectors.toSet());
}
}
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