* java.util.function.Function java.util.function.Function}.
 *
 * <p>The {@link Functions} class provides common functions and related utilities.
 *
 * <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/FunctionalExplained">the use of {@code Function}</a>.
 *
 * <h3>For Java 8+ users</h3>
 *

      Function<? super F, ? extends @Nullable T> function, Equivalence<T> resultEquivalence) {
    this.function = checkNotNull(function);
    this.resultEquivalence = checkNotNull(resultEquivalence);
  }

  @Override
  protected boolean doEquivalent(F a, F b) {
    return resultEquivalence.equivalent(function.apply(a), function.apply(b));
  }

  @Override
  protected int doHash(F a) {

  }

  /**
   * Returns a cache loader that uses {@code function} to load keys, without supporting either
   * reloading or bulk loading. This allows creating a cache loader using a lambda expression.
   *
   * <p>The returned object is serializable if {@code function} is serializable.
   *
   * @param function the function to be used for loading values; must never return {@code null}

          V,
          I extends Table<R, C, V>>
      Collector<T, ?, I> toTable(
          java.util.function.Function<? super T, ? extends R> rowFunction,
          java.util.function.Function<? super T, ? extends C> columnFunction,
          java.util.function.Function<? super T, ? extends V> valueFunction,
          java.util.function.Supplier<I> tableSupplier) {
    return TableCollectors.<T, R, C, V, I>toTable(
        rowFunction,

  private static <T> void testSuccessfulForwarding(
      Class<T> interfaceType, Method method, Function<? super T, ? extends T> wrapperFunction) {
    new InteractionTester<T>(interfaceType, method).testInteraction(wrapperFunction);
  }

  private static <T> void testExceptionPropagation(
      Class<T> interfaceType, Method method, Function<? super T, ? extends T> wrapperFunction) {
    RuntimeException exception = new RuntimeException();

  private static <T> void testSuccessfulForwarding(
      Class<T> interfaceType, Method method, Function<? super T, ? extends T> wrapperFunction) {
    new InteractionTester<T>(interfaceType, method).testInteraction(wrapperFunction);
  }

  private static <T> void testExceptionPropagation(
      Class<T> interfaceType, Method method, Function<? super T, ? extends T> wrapperFunction) {
    RuntimeException exception = new RuntimeException();

        });
  }

  private static final Function<Object, Optional<?>> NULLABLE_TO_OPTIONAL =
      new Function<Object, Optional<?>>() {
        @Override
        public Optional<?> apply(@Nullable Object obj) {
          return Optional.fromNullable(obj);
        }
      };

  private static final Function<Optional<?>, @Nullable Object> OPTIONAL_TO_NULLABLE =
      new Function<Optional<?>, @Nullable Object>() {

import java.util.AbstractCollection;
import java.util.Collection;
import java.util.Iterator;
import java.util.function.Function;

public class MappedCollection<U, V> extends AbstractCollection<U> {
    private final Collection<V> list;
    private final Function<V, U> mapper;

    public MappedCollection(Collection<V> list, Function<V, U> mapper) {
        this.list = list;
        this.mapper = mapper;
    }

    @Override

      }
    }
  }

  /**
   * Returns a function that delegates to the {@link Interner#intern} method of the given interner.
   *
   * @since 8.0
   */
  public static <E> Function<E, E> asFunction(Interner<E> interner) {
    return new InternerFunction<>(checkNotNull(interner));
  }

  private static class InternerFunction<E> implements Function<E, E> {

    private final Interner<E> interner;

  public void testAbsent() {
    assertEquals(
        "Map.merge(absent, value, function) should return value",
        v3(),
        getMap()
            .merge(
                k3(),
                v3(),
                (oldV, newV) -> {
                  throw new AssertionFailedError(
                      "Should not call merge function if key was absent");
                }));
    expectAdded(e3());
  }