001/*
002 * Java Genetic Algorithm Library (jenetics-8.1.0).
003 * Copyright (c) 2007-2024 Franz Wilhelmstötter
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * 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 * Author:
018 *    Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
019 */
020package io.jenetics.prog.op;
021
022import static java.util.Objects.requireNonNull;
023
024import java.util.function.BinaryOperator;
025import java.util.function.Function;
026import java.util.function.Supplier;
027import java.util.function.UnaryOperator;
028
029/**
030 * Operation interface. An operation is a function that maps some argument type
031 * with a given <em>arity</em> to a result object of the same type:
032 * {@code T[] -> T}.
033 *
034 * {@snippet lang="java":
035 * final Op<Double> add = Op.of("add", 2, v -> v[0] + v[1]);
036 * final Op<Double> add3 = Op.of("add3", 3, v -> v[0] + v[1] + v[2]);
037 * final Op<Double> sub = Op.of("sub", 2, v -> v[0] - v[1]);
038 * final Op<Double> sin = Op.of("sin", 1, v -> Math.sin(v[0]));
039 * }
040 *
041 * Implementations of the {@code Op} interface are usually immutable and doesn't
042 * maintain internal state. But some instances are ephemeral with changing state.
043 * This classes must override the {@link #get()} method inherited from the
044 * {@link Supplier} interface and return a new instance.
045 *
046 * @see Var
047 * @see Const
048 * @see EphemeralConst
049 *
050 * @param <T> the argument type of the operation
051 *
052 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
053 * @version 3.9
054 * @since 3.9
055 */
056public interface Op<T> extends Function<T[], T>, Supplier<Op<T>> {
057
058        /**
059         * Return the name of the operation.
060         *
061         * @return the name of the operation
062         */
063        String name();
064
065        /**
066         * Return the arity of the operation function. If the arity is zero, the
067         * operation is <em>terminal</em> operation.
068         *
069         * @return the arity of the operation
070         */
071        int arity();
072
073        /**
074         * Determines if the operation is a terminal operation.
075         *
076         * @return {@code true} if the operation is a terminal operation,
077         *         {@code false} otherwise
078         */
079        default boolean isTerminal() {
080                return arity() == 0;
081        }
082
083        /**
084         * Return {@code this} operation, or a new instance from the same type, if
085         * the operation needs to maintain internal state. This is essentially the
086         * case for ephemeral constants.
087         *
088         * @see EphemeralConst
089         *
090         * @return {@code this} operation, or a new instance
091         */
092        @Override
093        default Op<T> get() {
094                return this;
095        }
096
097        /**
098         * Create a new operation from the given parameter.
099         *
100         * @param name the operation name
101         * @param arity the arity of the operation
102         * @param function the function executed by the operation. In order to work
103         *        properly, the given function should be stateless and must not have
104         *        side effects.
105         * @param <T> the operation type
106         * @return a new operation from the given parameter
107         * @throws NullPointerException if the given {@code name} or {@code function}
108         *         is {@code null}
109         * @throws IllegalArgumentException if the given {@code arity} is smaller
110         *         than zero
111         */
112        static <T> Op<T> of(
113                final String name,
114                final int arity,
115                final Function<T[], T> function
116        ) {
117                return new Operation<>(name, arity, function);
118        }
119
120        /**
121         * Create a new operation with the given name and unary operation. The
122         * returned {@code Op} will have arity one.
123         *
124         * @since 4.0
125         *
126         * @param name the name of the returned operation
127         * @param function the used function of the operation
128         * @param <T> the operation type
129         * @return a new operation with the given name and unary operation
130         * @throws NullPointerException if the given {@code name} or {@code function}
131         *         is {@code null}
132         */
133        static <T> Op<T> of(
134                final String name,
135                final UnaryOperator<T> function
136        ) {
137                requireNonNull(function);
138                return of(name, 1, v -> function.apply(v[0]));
139        }
140
141        /**
142         * Create a new operation with the given name and binary operation. The
143         * returned {@code Op} will have arity two.
144         *
145         * @since 4.0
146         *
147         * @param name the name of the returned operation
148         * @param function the used function of the operation
149         * @param <T> the operation type
150         * @return a new operation with the given name and unary operation
151         * @throws NullPointerException if the given {@code name} or {@code function}
152         *         is {@code null}
153         */
154        static <T> Op<T> of(
155                final String name,
156                final BinaryOperator<T> function
157        ) {
158                requireNonNull(function);
159                return of(name, 2, v -> function.apply(v[0], v[1]));
160        }
161
162}