001 /*
002 * Java Genetic Algorithm Library (jenetics-6.1.0).
003 * Copyright (c) 2007-2020 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 */
020 package io.jenetics.prog.op;
021
022 import static java.util.Objects.requireNonNull;
023
024 import java.util.function.BinaryOperator;
025 import java.util.function.Function;
026 import java.util.function.Supplier;
027 import java.util.function.UnaryOperator;
028
029 /**
030 * Operation interface. An operation is a function which 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 * <pre>{@code
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 * }</pre>
040 *
041 * Implementations of the {@code Op} interface are usually immutable and doesn't
042 * maintain internal state. But some instance 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 */
056 public 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 }
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