001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017
018package org.apache.commons.lang3.function;
019
020import java.util.function.DoubleFunction;
021
022/**
023 * A functional interface like {@link DoubleFunction} that declares a {@link Throwable}.
024 *
025 * @param <R> Return type.
026 * @param <E> The kind of thrown exception or error.
027 * @since 3.11
028 */
029@FunctionalInterface
030public interface FailableDoubleFunction<R, E extends Throwable> {
031
032    /** NOP singleton */
033    @SuppressWarnings("rawtypes")
034    FailableDoubleFunction NOP = t -> null;
035
036    /**
037     * Returns The NOP singleton.
038     *
039     * @param <R> Return type.
040     * @param <E> The kind of thrown exception or error.
041     * @return The NOP singleton.
042     */
043    @SuppressWarnings("unchecked")
044    static <R, E extends Throwable> FailableDoubleFunction<R, E> nop() {
045        return NOP;
046    }
047
048    /**
049     * Applies this function.
050     *
051     * @param input the input for the function
052     * @return the result of the function
053     * @throws E Thrown when the function fails.
054     */
055    R apply(double input) throws E;
056}