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Java 8+ functional interfaces with checked exceptions support
There is a newer version: 1.6.1
/*
 * Copyright 2016 the original author or authors.
 *
 * Licensed 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 pl.touk.throwing;

import pl.touk.throwing.exception.WrappedException;

import java.util.Objects;
import java.util.Optional;
import java.util.function.Function;


/**
 * Represents a function that accepts one argument and returns a value;
 * Function might throw a checked exception instance.
 *
 * @param  the type of the input to the function
 * @param  the type of the result of the function
 * @param  the type of the thrown checked exception
 *
 */
@FunctionalInterface
public interface ThrowingFunction {
    R apply(T arg) throws E;

    /**
     * @param  type
     * @param  checked exception
     * @return a function that accepts one argument and returns it as a value.
     */
    static  ThrowingFunction identity() {
        return t -> t;
    }

    /**
     * @return a Function that returns the result of the given function as an Optional instance.
     * In case of a failure, empty Optional is returned
     */
    static  Function> lifted(ThrowingFunction f) {
        Objects.requireNonNull(f);

        return f.lift();
    }

    static  Function unchecked(ThrowingFunction f) {
        Objects.requireNonNull(f);

        return f.uncheck();
    }

    default  ThrowingFunction compose(final ThrowingFunction before) {
        Objects.requireNonNull(before);

        return (V v) -> apply(before.apply(v));
    }

    default  ThrowingFunction andThen(final ThrowingFunction after) {
        Objects.requireNonNull(after);

        return (T t) -> after.apply(apply(t));
    }

    /**
     * @return a Function that returns the result as an Optional instance. In case of a failure, empty Optional is
     * returned
     */
    default Function> lift() {
        return t -> {
            try {
                return Optional.of(apply(t));
            } catch (Throwable e) {
                return Optional.empty();
            }
        };
    }

    /**
     * @return a new Function instance which wraps thrown checked exception instance into a RuntimeException
     */
    default Function uncheck() {
        return t -> {
            try {
                return apply(t);
            } catch (final Throwable e) {
                throw new WrappedException(e);
            }
        };
    }
}