Add IntToIntFunction

src/changes/changes.xml

@@ -216,6 +216,7 @@ The <action> type attribute can be add,update,fix,remove.
     <action issue="LANG-1647" type="add" dev="ggregory" due-to="Arturo Bernal, Dimitrios Efthymiou, Gary Gregory">Add and ExceptionUtils.isChecked() and isUnchecked() #1069</action>
     <action                   type="add" dev="ggregory" due-to="Gary Gregory">Add and use ExceptionUtils.throwUnchecked(throwable).</action>
     <action                   type="add" dev="ggregory" due-to="Gary Gregory">Add LockingVisitors.create(O, ReadWriteLock).</action>
+    <action                   type="add" dev="ggregory" due-to="Gary Gregory">Add IntToIntFunction.</action>
     <!-- UPDATE -->
     <action                   type="update" dev="ggregory" due-to="Dependabot, XenoAmess, Gary Gregory">Bump actions/cache from 2.1.4 to 3.0.10 #742, #752, #764, #833, #867, #959, #964.</action>
     <action                   type="update" dev="ggregory" due-to="Dependabot, Gary Gregory">Bump actions/checkout from 2 to 3.1.0 #819, #825, #859, #963.</action>

src/main/java/org/apache/commons/lang3/function/IntToIntFunction.java

@@ -0,0 +1,52 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.commons.lang3.function;
+
+import java.util.function.Function;
+
+/**
+ * Represents a function that accepts an int-valued argument and produces an int-valued result. This is the {@code int}-to-{@code int} primitive specialization
+ * for {@link Function}.
+ *
+ * <p>
+ * This is a <a href="package-summary.html">functional interface</a> whose functional method is {@link #applyAsInt(int)}.
+ * </p>
+ *
+ * @see Function
+ * @since 3.13.0
+ */
+@FunctionalInterface
+public interface IntToIntFunction {
+
+    /**
+     * Returns a function that always returns its input argument.
+     *
+     * @return a function that always returns its input argument
+     */
+    static IntToIntFunction identity() {
+        return i -> i;
+    }
+
+    /**
+     * Applies this function to the given argument.
+     *
+     * @param value the function argument
+     * @return the function result
+     */
+    int applyAsInt(int value);
+}

src/test/java/org/apache/commons/lang3/function/IntToIntFunctionTest.java

@@ -0,0 +1,40 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.commons.lang3.function;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.apache.commons.lang3.AbstractLangTest;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests {@link IntToIntFunction}.
+ */
+public class IntToIntFunctionTest extends AbstractLangTest {
+
+    @Test
+    public void testApply() {
+        final IntToIntFunction func = i -> i + 1;
+        assertEquals(66, func.applyAsInt(65));
+    }
+
+    @Test
+    public void testIdentity() {
+        assertEquals(65, IntToIntFunction.identity().applyAsInt(65));
+    }
+}