001/* -*- mode: Java; c-basic-offset: 2; indent-tabs-mode: nil; coding: utf-8-unix -*-
002 *
003 * Copyright © 2023–2025 microBean™.
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
006 * the License. You may obtain a copy of the License at
007 *
008 *     http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
011 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
012 * specific language governing permissions and limitations under the License.
013 */
014package org.microbean.scopelet;
015
016import java.lang.constant.ClassDesc;
017import java.lang.constant.Constable;
018import java.lang.constant.ConstantDesc;
019import java.lang.constant.DynamicConstantDesc;
020import java.lang.constant.MethodHandleDesc;
021
022import java.util.List;
023import java.util.Objects;
024import java.util.Optional;
025
026import org.microbean.bean.Id;
027
028import org.microbean.construct.Domain;
029
030import static java.lang.constant.ConstantDescs.BSM_INVOKE;
031
032import static org.microbean.assign.Qualifiers.anyQualifier;
033
034import static org.microbean.scope.Scope.SINGLETON_ID;
035
036/**
037 * A {@link MapBackedScopelet} implementation that caches singletons.
038 *
039 * @author <a href="https://about.me/lairdnelson" target="_top">Laird Nelson</a>
040 */
041public class SingletonScopelet extends MapBackedScopelet<SingletonScopelet> implements Constable {
042
043  private final Domain domain;
044
045  /**
046   * Creates a new {@link SingletonScopelet}.
047   *
048   * @param domain a {@link Domain}; must not be {@code null}
049   *
050   * @exception NullPointerException if {@code domain} is {@code null}
051   */
052  public SingletonScopelet(final Domain domain) {
053    super(SINGLETON_ID); // the scope we implement
054    this.domain = Objects.requireNonNull(domain, "domain");
055  }
056
057  @Override // Scopelet<SingletonScopelet>
058  public Id id() {
059    return
060      new Id(List.of(this.domain.declaredType(SingletonScopelet.class.getName()),
061                     this.domain.declaredType(null,
062                                              this.domain.typeElement(Scopelet.class.getName()),
063                                              this.domain.declaredType(SingletonScopelet.class.getName()))),
064             List.of(SINGLETON_ID, anyQualifier()), // qualifiers
065             SINGLETON_ID); // the scope we belong to
066  }
067
068  @Override // Constable
069  public Optional<? extends ConstantDesc> describeConstable() {
070    return (this.domain instanceof Constable c ? c.describeConstable() : Optional.<ConstantDesc>empty())
071      .map(domainDesc -> DynamicConstantDesc.of(BSM_INVOKE,
072                                             MethodHandleDesc.ofConstructor(ClassDesc.of(this.getClass().getName()),
073                                                                            ClassDesc.of(Domain.class.getName())),
074                                             domainDesc));
075  }
076
077}