001/*
002 * Java Genetic Algorithm Library (jenetics-7.2.0).
003 * Copyright (c) 2007-2023 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.lang.String.format;
023import static java.util.Objects.requireNonNull;
024import static io.jenetics.internal.util.SerialIO.readNullableString;
025import static io.jenetics.internal.util.SerialIO.writeNullableString;
026
027import java.io.IOException;
028import java.io.InvalidObjectException;
029import java.io.ObjectInput;
030import java.io.ObjectInputStream;
031import java.io.ObjectOutput;
032import java.io.Serial;
033import java.io.Serializable;
034import java.util.Objects;
035import java.util.function.Supplier;
036
037import io.jenetics.internal.util.Lazy;
038
039/**
040 * Implementation of an <em>ephemeral</em> constant. It causes the insertion of
041 * a <em>mutable</em> constant into the operation tree. Every time this terminal
042 * is chosen, a different value is generated which is then used for that
043 * particular terminal, and which will remain fixed for the given tree. The main
044 * usage would be to introduce random terminal values.
045 *
046 * <pre>{@code
047 * final Random random = ...;
048 * final Op<Double> val = EphemeralConst.of(random::nextDouble);
049 * }</pre>
050 *
051 * <b>Serialization</b>
052 * Although the {@code EphemeralConst} class implements the {@link Serializable}
053 * interface, the serialization will fail if the <em>const</em> supplier is not
054 * <em>serializable</em> as well. This can be achieved by <em>casting</em> the
055 * supplier to a {@link Serializable}.
056 * <pre>{@code
057 * final Random random = new Random();
058 * final EphemeralConst<Integer> object = EphemeralConst.of(
059 *     "R",
060 *     (Supplier<Integer> & Serializable)random::nextInt
061 * );
062 * }</pre>
063 * The serialization of the <em>constant</em> will fail, if the lambda has to
064 * capture variables form a <em>non</em>-serializable context (class). In such a
065 * case, it is advisable to create a dedicated supplier class.
066 * <pre>{@code
067 * final class RandomInt implements Supplier<Integer>, Serializable {
068 *     private final Random rnd = new Random();
069 *     private final int min;
070 *     private final int max;
071 *
072 *     private RandomInt(final int min, final int max) {
073 *         this.min = min;
074 *         this.max = max;
075 *     }
076 *
077 *     \@Override
078 *     public Integer get() {
079 *         return rnd.nextInt(max - min) + min;
080 *     }
081 * }
082 * }</pre>
083 *
084 *
085 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
086 * @version 7.0
087 * @since 3.9
088 */
089public final class EphemeralConst<T>
090        extends Val<T>
091        implements Op<T>, Serializable
092{
093
094        @Serial
095        private static final long serialVersionUID = 1L;
096
097        private final Lazy<T> _value;
098        private final Supplier<T> _supplier;
099
100        private EphemeralConst(
101                final String name,
102                final Lazy<T> value,
103                final Supplier<T> supplier
104        ) {
105                super(name);
106                _value = requireNonNull(value);
107                _supplier = requireNonNull(supplier);
108        }
109
110        private EphemeralConst(final String name, final Supplier<T> supplier) {
111                this(name, Lazy.of(supplier), supplier);
112        }
113
114        /**
115         * Return a newly created, uninitialized constant of type {@code T}.
116         *
117         * @return a newly created, uninitialized constant of type {@code T}
118         */
119        @Override
120        public Op<T> get() {
121                return new EphemeralConst<>(name(), _supplier);
122        }
123
124        /**
125         * Fixes and returns the constant value.
126         *
127         * @since 5.0
128         *
129         * @return the constant value
130         */
131        @Override
132        public T value() {
133                return _value.get();
134        }
135
136        @Override
137        public String toString() {
138                return name() != null
139                        ? format("%s(%s)", name(), value())
140                        : Objects.toString(value());
141        }
142
143        /**
144         * Create a new ephemeral constant with the given {@code name} and value
145         * {@code supplier}. For every newly created operation tree, a new constant
146         * value is chosen for this terminal operation. The value is then kept
147         * constant for this tree.
148         *
149         * @param name the name of the ephemeral constant
150         * @param supplier the value supplier
151         * @param <T> the constant type
152         * @return a new ephemeral constant
153         * @throws NullPointerException if one of the arguments is {@code null}
154         */
155        public static <T> EphemeralConst<T> of(
156                final String name,
157                final Supplier<T> supplier
158        ) {
159                return new EphemeralConst<>(requireNonNull(name), supplier);
160        }
161
162        /**
163         * Create a new ephemeral constant with the given value {@code supplier}.
164         * For every newly created operation tree, a new constant value is chosen
165         * for this terminal operation. The value is then kept constant for this tree.
166         *
167         * @param supplier the value supplier
168         * @param <T> the constant type
169         * @return a new ephemeral constant
170         * @throws NullPointerException if the {@code supplier} is {@code null}
171         */
172        public static <T> EphemeralConst<T> of(final Supplier<T> supplier) {
173                return new EphemeralConst<>(null, supplier);
174        }
175
176
177        /* *************************************************************************
178         *  Java object serialization
179         * ************************************************************************/
180
181        @Serial
182        private Object writeReplace() {
183                return new SerialProxy(SerialProxy.EPHEMERAL_CONST, this);
184        }
185
186        @Serial
187        private void readObject(final ObjectInputStream stream)
188                throws InvalidObjectException
189        {
190                throw new InvalidObjectException("Serialization proxy required.");
191        }
192
193        void write(final ObjectOutput out) throws IOException {
194                writeNullableString(name(), out);
195                out.writeObject(value());
196                out.writeObject(_supplier);
197        }
198
199        @SuppressWarnings({"unchecked", "rawtypes"})
200        static EphemeralConst read(final ObjectInput in)
201                throws IOException, ClassNotFoundException
202        {
203                final String name = readNullableString(in);
204                final Object value = in.readObject();
205                final Supplier supplier = (Supplier)in.readObject();
206
207                return new EphemeralConst(name, Lazy.ofValue(value), supplier);
208        }
209
210}