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Apache Commons Lang, a package of Java utility classes for the classes that are in java.lang's hierarchy, or are considered to be so standard as to justify existence in java.lang. The code is tested using the latest revision of the JDK for supported LTS releases: 8, 11, 17 and 21 currently. See https://github.com/apache/commons-lang/blob/master/.github/workflows/maven.yml Please ensure your build environment is up-to-date and kindly report any build issues.

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/*
 * 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.Objects;
import java.util.function.DoubleUnaryOperator;

/**
 * A functional interface like {@link DoubleUnaryOperator} that declares a {@link Throwable}.
 *
 * @param  The kind of thrown exception or error.
 * @since 3.11
 */
public interface FailableDoubleUnaryOperator {

    /** NOP singleton */
    @SuppressWarnings("rawtypes")
    FailableDoubleUnaryOperator NOP = t -> 0d;

    /**
     * Returns a unary operator that always returns its input argument.
     *
     * @param  The kind of thrown exception or error.
     * @return a unary operator that always returns its input argument
     */
    static  FailableDoubleUnaryOperator identity() {
        return t -> t;
    }

    /**
     * Returns The NOP singleton.
     *
     * @param  The kind of thrown exception or error.
     * @return The NOP singleton.
     */
    @SuppressWarnings("unchecked")
    static  FailableDoubleUnaryOperator nop() {
        return NOP;
    }

    /**
     * Returns a composed {@link FailableDoubleUnaryOperator} like
     * {@link DoubleUnaryOperator#andThen(DoubleUnaryOperator)}.
     *
     * @param after the operator to apply after this one.
     * @return a composed {@link FailableDoubleUnaryOperator} like
     *         {@link DoubleUnaryOperator#andThen(DoubleUnaryOperator)}.
     * @throws NullPointerException if after is null.
     * @see #compose(FailableDoubleUnaryOperator)
     */
    default FailableDoubleUnaryOperator andThen(final FailableDoubleUnaryOperator after) {
        Objects.requireNonNull(after);
        return (final double t) -> after.applyAsDouble(applyAsDouble(t));
    }

    /**
     * Applies this operator to the given operand.
     *
     * @param operand the operand
     * @return the operator result
     * @throws E Thrown when a consumer fails.
     */
    double applyAsDouble(double operand) throws E;

    /**
     * Returns a composed {@link FailableDoubleUnaryOperator} like
     * {@link DoubleUnaryOperator#compose(DoubleUnaryOperator)}.
     *
     * @param before the operator to apply before this one.
     * @return a composed {@link FailableDoubleUnaryOperator} like
     *         {@link DoubleUnaryOperator#compose(DoubleUnaryOperator)}.
     * @throws NullPointerException if before is null.
     * @see #andThen(FailableDoubleUnaryOperator)
     */
    default FailableDoubleUnaryOperator compose(final FailableDoubleUnaryOperator before) {
        Objects.requireNonNull(before);
        return (final double v) -> applyAsDouble(before.applyAsDouble(v));
    }
}