added PermutationBinaryOperator

Author: cicirello

src/main/java/org/cicirello/permutations/Permutation.java

@@ -216,6 +216,19 @@ public void apply(PermutationUnaryOperator operator) {
 		operator.apply(permutation);
 	}
 
+	/**
+	 * Applies a custom binary operator on a pair of Permutation objects.
+	 * The raw int array belonging to this is passed as the first array to
+	 * operator.apply() and the raw int array belonging to other is passed
+	 * as the second.
+	 *
+	 * @param operator A binary Permutation operator
+	 * @param other The other Permutation
+	 */
+	public void apply(PermutationBinaryOperator operator, Permutation other) {
+		operator.apply(permutation, other.permutation);
+	}
+	
 	/**
 	 * Creates an identical copy of this object.
 	 * @return an identical copy of this object

src/main/java/org/cicirello/permutations/PermutationBinaryOperator.java

@@ -0,0 +1,50 @@
+/*
+ * JavaPermutationTools: A Java library for computation on permutations and sequences
+ * Copyright 2005-2022 Vincent A. Cicirello, <https://www.cicirello.org/>.
+ *
+ * This file is part of JavaPermutationTools (https://jpt.cicirello.org/).
+ *
+ * JavaPermutationTools is free software: you can 
+ * redistribute it and/or modify it under the terms of the GNU 
+ * General Public License as published by the Free Software 
+ * Foundation, either version 3 of the License, or (at your 
+ * option) any later version.
+ *
+ * JavaPermutationTools is distributed in the hope 
+ * that it will be useful, but WITHOUT ANY WARRANTY; without even 
+ * the implied warranty of MERCHANTABILITY or FITNESS FOR A 
+ * PARTICULAR PURPOSE.  See the GNU General Public License for more 
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with JavaPermutationTools.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.cicirello.permutations;
+
+/**
+ * A functional interface for defining custom binary operators on Permutations.
+ * See the {@link Permutation#apply(PermutationBinaryOperator,Permutation)} method.
+ *
+ * @author <a href=https://www.cicirello.org/ target=_top>Vincent A. Cicirello</a>, 
+ * <a href=https://www.cicirello.org/ target=_top>https://www.cicirello.org/</a> 
+ */
+@FunctionalInterface
+public interface PermutationBinaryOperator {
+	
+	/**
+	 * Applies an operator on the raw representations of
+	 * a pair of Permutations. Implementers of this interface are responsible
+	 * for ensuring that the apply method maintains valid
+	 * permutations of the integers in {0, 1, ..., rawPermutation1.length - 1 },
+	 * and likewise for rawPermutation2.
+	 *
+	 * @param rawPermutation1 A reference to the raw array of ints underlying a
+	 * Permutation object. Changes to this array will directly change the Permutation
+	 * object that encapsulates it.
+	 *
+	 * @param rawPermutation2 A reference to the raw array of ints underlying a
+	 * Permutation object. Changes to this array will directly change the Permutation
+	 * object that encapsulates it.
+	 */
+	void apply(int[] rawPermutation1, int[] rawPermutation2);
+}