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.Objects;
021import java.util.function.Function;
022
023/**
024 * A functional interface like {@link Function} that declares a {@link Throwable}.
025 *
026 * @param <T> Input type 1.
027 * @param <R> Return type.
028 * @param <E> The kind of thrown exception or error.
029 * @since 3.11
030 */
031@FunctionalInterface
032public interface FailableFunction<T, R, E extends Throwable> {
033
034    /** NOP singleton */
035    @SuppressWarnings("rawtypes")
036    FailableFunction NOP = t -> null;
037
038    /**
039     * Starts a fluent chain like {@code function(foo::bar).andThen(...).andThen(...).apply(...);}
040     *
041     * @param <T> Input type.
042     * @param <R> Return type.
043     * @param <E> The kind of thrown exception or error.
044     * @param function   the argument to return.
045     * @return the argument
046     * @since 3.14.0
047     */
048    static <T, R, E extends Throwable> FailableFunction<T, R, E> function(final FailableFunction<T, R, E> function) {
049        return function;
050    }
051
052    /**
053     * Returns a function that always returns its input argument.
054     *
055     * @param <T> the type of the input and output objects to the function
056     * @param <E> The kind of thrown exception or error.
057     * @return a function that always returns its input argument
058     */
059    static <T, E extends Throwable> FailableFunction<T, T, E> identity() {
060        return t -> t;
061    }
062
063    /**
064     * Returns The NOP singleton.
065     *
066     * @param <T> Consumed type.
067     * @param <R> Return type.
068     * @param <E> The kind of thrown exception or error.
069     * @return The NOP singleton.
070     */
071    @SuppressWarnings("unchecked")
072    static <T, R, E extends Throwable> FailableFunction<T, R, E> nop() {
073        return NOP;
074    }
075
076    /**
077     * Returns a composed {@link FailableFunction} like {@link Function#andThen(Function)}.
078     *
079     * @param <V> the output type of the {@code after} function, and of the composed function.
080     * @return a composed {@link FailableFunction} like {@link Function#andThen(Function)}.
081     * @param after the operation to perform after this one.
082     * @throws NullPointerException when {@code after} is null.
083     */
084    default <V> FailableFunction<T, V, E> andThen(final FailableFunction<? super R, ? extends V, E> after) {
085        Objects.requireNonNull(after);
086        return (final T t) -> after.apply(apply(t));
087    }
088
089    /**
090     * Applies this function.
091     *
092     * @param input the input for the function
093     * @return the result of the function
094     * @throws E Thrown when the function fails.
095     */
096    R apply(T input) throws E;
097
098    /**
099     * Returns a composed {@link FailableFunction} like {@link Function#compose(Function)}.
100     *
101     * @param <V> the input type to the {@code before} function, and to the composed function.
102     * @param before the operator to apply before this one.
103     * @return a composed {@link FailableFunction} like {@link Function#compose(Function)}.
104     * @throws NullPointerException if before is null.
105     * @see #andThen(FailableFunction)
106     */
107    default <V> FailableFunction<V, R, E> compose(final FailableFunction<? super V, ? extends T, E> before) {
108        Objects.requireNonNull(before);
109        return (final V v) -> apply(before.apply(v));
110    }
111}