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.base;
  
  import java.util.Optional;
  import java.util.function.Supplier;
  
  import org.springframework.util.function.ThrowingSupplier;
  
  /**
   * <h1>- internal use only -</h1>
   * <p>
   * (non-thread-safe) Supplier with memoization.
   * </p>
   * <p>
   * <b>WARNING</b>: Do <b>NOT</b> use any of the classes provided by this package! <br/>
   * These may be changed or removed without notice!
   * </p>
   *
   * @since 2.0
   */
  public interface _Lazy<T> extends Supplier<T> {
  
      // -- INTERFACE
  
      /**
       * @return whether this lazy got initialized and holds a memoized value
       */
      public boolean isMemoized();
  
      /**
       * Clears the lazy's memoized value. Resets this lazy to its initial state.<br>
       * isMemoized() = false;
       *
       */
      public void clear();
  
      /**
       * Evaluates this lazy value and memoizes it, when called the first time
       * after initialization or clear().
       * <p>
       * Postcondition when memoization throws an exception: isMemoized()->true and get()->null.
       * In other words: the _Lazy needs to be cleared before it can be re-memoized.
       */
      @Override
      public T get();
  
      /**
       * Optionally returns the value, based on whether this lazy got initialized and holds a memoized value.
       */
      public Optional<T> getMemoized();
  
      /**
       * Sets the memoized value, if not already memoized.
       * @param value
       * @throws IllegalStateException if already memoized
       */
      public void set(T value);
  
      // -- FACTORIES
  
      /**
       * Concurrent calls to this lazy's get() method might result in concurrent calls to the
       * specified {@code supplier}.
       * @param supplier
       * @return an (non-thread-safe) instance of _Lazy that initializes with the specified {@code supplier}
       */
      public static <T> _Lazy<T> of(final ThrowingSupplier<? extends T> supplier) {
          return new _Lazy_Simple<T>(supplier);
      }
  
      /**
       * Thread-safe variant to {@link _Lazy#of(ThrowingSupplier)}.
       * <p>
       * Concurrent calls to this lazy's get() method will never result in concurrent calls to the
       * specified {@code supplier}.
       * @param supplier
       * @return an (thread-safe) instance of _Lazy that initializes with the specified {@code supplier}
       */
      public static <T> _Lazy<T> threadSafe(final ThrowingSupplier<? extends T> supplier) {
          return new _Lazy_ThreadSafe<T>(supplier);
      }
  
  }
  