content: /*
   *  Licensed to the Apache Software Foundation (ASF) under one
   *  or more contributor license agreements.  See the NOTICE file
   *  distributed with this work for additional information
   *  regarding copyright ownership.  The ASF licenses this file
   *  to you 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.apache.causeway.commons.internal.ref;
  
  import java.io.Serializable;
  import java.util.function.Supplier;
  import java.util.function.UnaryOperator;
  
  import org.jspecify.annotations.Nullable;
  
  import lombok.Getter;
  
  /**
   * non thread-safe
   */
  public final class TransientObjectRef<T> implements Serializable {
  
      private static final long serialVersionUID = 1L;
  
      @Getter
      private transient @Nullable T object;
      private transient boolean updating;
  
      public TransientObjectRef(@Nullable final T object) {
          this.object = object;
      }
  
      public T computeIfAbsent(final Supplier<T> supplier) {
          return object!=null
              ? object
              : update(__->supplier.get());
      }
  
      /**
       * the updater itself must not directly modify this TransientObjectRef instance
       */
      public T update(final UnaryOperator<T> updater) {
          if(updating) {
              throw new UnsupportedOperationException("nested call to update detected");
          }
          this.updating = true;
          try {
              this.object = updater.apply(object);
          } finally {
              this.updating = false;
          }
          return object;
      }
  
      @Override
      public String toString() {
          return "TransientObjectRef[%s]".formatted(object!=null ? "PRESENT" : "EMPTY");
      }
  
  }
  