Added more efficient constructor to array-based sets

CHANGES

@@ -4,7 +4,7 @@
   was allowing a load factor of 1. Thanks to Andy Clegg for
   reporting this bug.
 
-- The copy constructor of array-based maps are now more efficient.
+- The copy constructor of array-based containers are now more efficient.
   Thanks to Vladimir Krivosheev for proposing this enhancement.
 
 8.3.1

drv/ArraySet.drv

@@ -19,6 +19,7 @@ package PACKAGE;
 
 import java.util.Collection;
 import java.util.NoSuchElementException;
+import java.util.Set;
 
 /** A simple, brute-force implementation of a set based on a backing array.
  *
@@ -72,6 +73,32 @@ public class ARRAY_SET KEY_GENERIC extends ABSTRACT_SET KEY_GENERIC implements j
 		addAll(c);
 	}
 
+	/** Creates a new array set copying the contents of a given collection.
+	 * @param c a collection.
+	 */
+	public ARRAY_SET(SET KEY_GENERIC c) {
+		this(c.size());
+		int i = 0;
+		for(KEY_TYPE x : c) {
+			a[i] = x;
+			i++;
+		}
+		size = i;
+	}
+
+	/** Creates a new array set copying the contents of a given set.
+	 * @param c a collection.
+	 */
+	public ARRAY_SET(final Set<? extends KEY_GENERIC_CLASS> c) {
+		this(c.size());
+		int i = 0;
+		for(KEY_GENERIC_CLASS x: c) {
+			a[i] = KEY_CLASS2TYPE(x);
+			i++;
+		}
+		size = i;
+	}
+
 
 	/** Creates a new array set using the given backing array and the given number of elements of the array.
 	 *

test/it/unimi/dsi/fastutil/ints/Int2IntArrayMapTest.java

@@ -0,0 +1,32 @@
+package it.unimi.dsi.fastutil.ints;
+
+/*
+ * Copyright (C) 2020 Sebastiano Vigna
+ *
+ * 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.
+ */
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.HashMap;
+
+import org.junit.Test;
+
+public class Int2IntArrayMapTest {
+	@Test
+	public void testCopyConstructor() {
+		final Int2IntOpenHashMap m = new Int2IntOpenHashMap(new int [] {1, 2}, new int[] {3, 4});
+		assertEquals(new Int2IntArrayMap(m), m);
+		assertEquals(new HashMap<>(m), m);
+	}
+}

test/it/unimi/dsi/fastutil/ints/IntArraySetTest.java

@@ -16,23 +16,31 @@
  * limitations under the License.
  */
 
-import it.unimi.dsi.fastutil.ints.IntArraySet;
-import it.unimi.dsi.fastutil.ints.IntOpenHashSet;
-import it.unimi.dsi.fastutil.io.BinIO;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
 
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.ObjectOutputStream;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.HashSet;
 
 import org.junit.Test;
 
-import static org.junit.Assert.*;
+import it.unimi.dsi.fastutil.io.BinIO;
 
 public class IntArraySetTest {
 
+	@Test
+	public void testCopyConstructor() {
+		final IntOpenHashSet s = new IntOpenHashSet(new int[] { 1, 2 });
+		assertEquals(new IntArraySet(s), s);
+		assertEquals(new HashSet<>(s), s);
+	}
+
 	@SuppressWarnings("boxing")
 	@Test
 	public void testNullInEquals() {
@@ -70,7 +78,7 @@ public void testSet() {
 
 	@Test
 	public void testClone() {
-		IntArraySet s = new IntArraySet();
+		final IntArraySet s = new IntArraySet();
 		assertEquals(s, s.clone());
 		s.add(0);
 		assertEquals(s, s.clone());
@@ -86,8 +94,8 @@ public void testClone() {
 
 	@Test
 	public void testSerialisation() throws IOException, ClassNotFoundException {
-		IntArraySet s = new IntArraySet();
-		ByteArrayOutputStream baos = new ByteArrayOutputStream();
+		final IntArraySet s = new IntArraySet();
+		final ByteArrayOutputStream baos = new ByteArrayOutputStream();
 		ObjectOutputStream oos = new ObjectOutputStream(baos);
 		oos.writeObject(s);
 		oos.close();