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Highly configurable message format library supporting message definition through annotations

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/*
 * Copyright 2023 Jeroen Gremmen
 *
 * Licensed 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
 *
 *   https://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 de.sayayi.lib.message.util;

import org.jetbrains.annotations.Contract;
import org.jetbrains.annotations.NotNull;

import java.util.function.Supplier;


/**
 * This supplier implementation delegates to another supplier and caches the supplied value, thus
 * invoking the delegated supplier only once.
 *
 * @param   supplier value type
 *
 * @author Jeroen Gremmen
 * @since 0.8.0
 */
public final class SupplierDelegate implements Supplier
{
  private Supplier supplier;
  private T value;


  private SupplierDelegate(@NotNull Supplier supplier) {
    this.supplier = supplier;
  }


  @Override
  public T get()
  {
    if (supplier != null)
    {
      value = supplier.get();
      supplier = null;  // drop supplier; we don't need it anymore
    }

    return value;
  }


  /**
   * Creates a supplier delegate with the given {@code supplier}.
   *
   * @param supplier  supplier to delegate to, not {@code null}
   *
   * @return  supplier delegate instance, never {@code null}
   *
   * @param   supplier value type
   */
  @Contract(value = "_ -> new", pure = true)
  public static  @NotNull Supplier of(@NotNull Supplier supplier) {
    return new SupplierDelegate<>(supplier);
  }
}