    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}