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Specializations and support utilities for functional interfaces that are missing from the standard library
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// SPDX-License-Identifier: Apache-2.0
/*
 * extended-functions
 * Copyright 2021-2024 Marko Zajc
 *
 * 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 org.eu.zajc.ef.unary;

import java.util.Objects;
import java.util.function.UnaryOperator;

import javax.annotation.Nonnull;

import org.eu.zajc.ef.binary.CharBinaryOperator;

/**
 * Represents an operation on a single {@code char}-valued operand that produces an
 * {@code char}-valued result. This is the primitive type specialization of
 * {@link UnaryOperator} for {@code char}.
 *
 * 
 * This is a functional interface whose functional method is
 * {@link #applyAsChar(char)}.
 *
 * @see UnaryOperator
 * @see CharBinaryOperator
 *
 * @author Marko Zajc
 */
public interface CharUnaryOperator {

	/**
	 * Applies this operator to the given operand.
	 *
	 * @param operand
	 *            the operand
	 *
	 * @return the operator result
	 */
	char applyAsChar(char operand);

	/**
	 * Returns a composed operator that first applies the {@code before} operator to its
	 * input, and then applies this operator to the result. If evaluation of either
	 * operator throws an exception, it is relayed to the caller of the composed
	 * operator.
	 *
	 * @param before
	 *            the operator to apply before this operator is applied
	 *
	 * @return a composed operator that first applies the {@code before} operator and
	 *         then applies this operator
	 *
	 * @throws NullPointerException
	 *             if before is null
	 *
	 * @see #andThen(CharUnaryOperator)
	 */
	@Nonnull
	default CharUnaryOperator compose(@Nonnull CharUnaryOperator before) {
		Objects.requireNonNull(before);
		return (char v) -> applyAsChar(before.applyAsChar(v));
	}

	/**
	 * Returns a composed operator that first applies this operator to its input, and
	 * then applies the {@code after} operator to the result. If evaluation of either
	 * operator throws an exception, it is relayed to the caller of the composed
	 * operator.
	 *
	 * @param after
	 *            the operator to apply after this operator is applied
	 *
	 * @return a composed operator that first applies this operator and then applies the
	 *         {@code after} operator
	 *
	 * @throws NullPointerException
	 *             if after is null
	 *
	 * @see #compose(CharUnaryOperator)
	 */
	@Nonnull
	default CharUnaryOperator andThen(@Nonnull CharUnaryOperator after) {
		Objects.requireNonNull(after);
		return (char t) -> after.applyAsChar(applyAsChar(t));
	}

	/**
	 * Returns a unary operator that always returns its input argument.
	 *
	 * @return a unary operator that always returns its input argument
	 */
	@Nonnull
	static CharUnaryOperator identity() {
		return t -> t;
	}

}