// Path: src/main/java/com/fernandocejas/arrow/functions/Function.java
// public interface Function<F, T> {
//   /**
//    * Returns the result of applying this function to {@code input}. This method is <i>generally
//    * expected</i>, but not absolutely required, to have the following properties:
//    *
//    * <ul>
//    * <li>Its execution does not cause any observable side effects.
//    * <li>The computation is <i>consistent with equals</i>.
//    * Objects.equal}{@code (a, b)} implies that {@code Objects.equal(function.apply(a),
//    * function.apply(b))}.
//    * </ul>
//    *
//    * @throws NullPointerException if {@code input} is null
//    */
//   @Nullable T apply(F input);
// 
//   /**
//    * Indicates whether another object is equal to this function.
//    *
//    * <p>Most implementations will have no reason to override the behavior of {@link Object#equals}.
//    * However, an implementation may also choose to return {@code true} whenever {@code object} is a
//    * {@link Function} that it considers <i>interchangeable</i> with this one. "Interchangeable"
//    * <i>typically</i> means that {@code Objects.equal(this.apply(f), that.apply(f))} is true for
//    * all
//    * {@code f} of type {@code F}. Note that a {@code false} result from this method does not imply
//    * that the functions are known <i>not</i> to be interchangeable.
//    */
//   @Override boolean equals(@Nullable Object object);
// }
// 
// Path: src/main/java/com/fernandocejas/arrow/checks/Preconditions.java
// public static <T> T checkNotNull(T reference) {
//   if (reference == null) {
//     throw new NullPointerException();
//   }
//   return reference;
// }


import com.fernandocejas.arrow.functions.Function;
import java.util.Collections;
import java.util.Set;
import org.jetbrains.annotations.Nullable;
import static com.fernandocejas.arrow.checks.Preconditions.checkNotNull;
/**
 * Copyright (C) 2011 The Guava Authors
 *
 * 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
 *
 * 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 com.fernandocejas.arrow.optional;



/**
 * Implementation of an {@link Optional} not containing a reference.
 *
 * <p><b>This class contains code derived from <a href="https://github.com/google/guava">Google
 * Guava</a></b>
 */
final class Absent<T> extends Optional<T> {
  private static final long serialVersionUID = 0;

  static final Absent<Object> INSTANCE = new Absent<>();

  @SuppressWarnings("unchecked") // implementation is "fully variant"
  static <T> Optional<T> withType() {
    return (Optional<T>) INSTANCE;
  }

  private Absent() {
  }

  @Override
  public boolean isPresent() {
    return false;
  }

  @Override
  public T get() {
    throw new IllegalStateException("Optional.get() cannot be called on an absent value");
  }

  @Override
  public T or(T defaultValue) {
// Path: src/main/java/com/fernandocejas/arrow/functions/Function.java
// public interface Function<F, T> {
//   /**
//    * Returns the result of applying this function to {@code input}. This method is <i>generally
//    * expected</i>, but not absolutely required, to have the following properties:
//    *
//    * <ul>
//    * <li>Its execution does not cause any observable side effects.
//    * <li>The computation is <i>consistent with equals</i>.
//    * Objects.equal}{@code (a, b)} implies that {@code Objects.equal(function.apply(a),
//    * function.apply(b))}.
//    * </ul>
//    *
//    * @throws NullPointerException if {@code input} is null
//    */
//   @Nullable T apply(F input);
// 
//   /**
//    * Indicates whether another object is equal to this function.
//    *
//    * <p>Most implementations will have no reason to override the behavior of {@link Object#equals}.
//    * However, an implementation may also choose to return {@code true} whenever {@code object} is a
//    * {@link Function} that it considers <i>interchangeable</i> with this one. "Interchangeable"
//    * <i>typically</i> means that {@code Objects.equal(this.apply(f), that.apply(f))} is true for
//    * all
//    * {@code f} of type {@code F}. Note that a {@code false} result from this method does not imply
//    * that the functions are known <i>not</i> to be interchangeable.
//    */
//   @Override boolean equals(@Nullable Object object);
// }
// 
// Path: src/main/java/com/fernandocejas/arrow/checks/Preconditions.java
// public static <T> T checkNotNull(T reference) {
//   if (reference == null) {
//     throw new NullPointerException();
//   }
//   return reference;
// }


// Path: src/main/java/com/fernandocejas/arrow/optional/Absent.java
import com.fernandocejas.arrow.functions.Function;
import java.util.Collections;
import java.util.Set;
import org.jetbrains.annotations.Nullable;
import static com.fernandocejas.arrow.checks.Preconditions.checkNotNull;

/**
 * Copyright (C) 2011 The Guava Authors
 *
 * 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
 *
 * 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 com.fernandocejas.arrow.optional;



/**
 * Implementation of an {@link Optional} not containing a reference.
 *
 * <p><b>This class contains code derived from <a href="https://github.com/google/guava">Google
 * Guava</a></b>
 */
final class Absent<T> extends Optional<T> {
  private static final long serialVersionUID = 0;

  static final Absent<Object> INSTANCE = new Absent<>();

  @SuppressWarnings("unchecked") // implementation is "fully variant"
  static <T> Optional<T> withType() {
    return (Optional<T>) INSTANCE;
  }

  private Absent() {
  }

  @Override
  public boolean isPresent() {
    return false;
  }

  @Override
  public T get() {
    throw new IllegalStateException("Optional.get() cannot be called on an absent value");
  }

  @Override
  public T or(T defaultValue) {
    return checkNotNull(defaultValue, "use Optional.orNull() instead of Optional.or(null)");