@DoNotMock("Use Interners.new*Interner")
@J2ktIncompatible
@GwtIncompatible
public interface Interner<E> {
  /**
   * Chooses and returns the representative instance for any of a collection of instances that are
   * equal to each other. If two {@linkplain Object#equals equal} inputs are given to this method,
   * both calls will return the same instance. That is, {@code intern(a).equals(a)} always holds,

@DoNotMock("Use Interners.new*Interner")
@J2ktIncompatible
@GwtIncompatible
public interface Interner<E> {
  /**
   * Chooses and returns the representative instance for any of a collection of instances that are
   * equal to each other. If two {@linkplain Object#equals equal} inputs are given to this method,
   * both calls will return the same instance. That is, {@code intern(a).equals(a)} always holds,

   * 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 final class InternerFunction<E> implements Function<E, E> {

    private final Interner<E> interner;

    InternerFunction(Interner<E> interner) {

  @Benchmark
  int weakInterner(int reps) {
    Interner<String> interner = Interners.newWeakInterner();
    for (int i = 0; i < reps; i++) {
      String unused = interner.intern(Double.toHexString(Math.random()));
    }
    return reps;
  }

  @CanIgnoreReturnValue
  @Benchmark
  int strongInterner(int reps) {
    Interner<String> interner = Interners.newStrongInterner();
    for (int i = 0; i < reps; i++) {

   * 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 final class InternerFunction<E> implements Function<E, E> {

    private final Interner<E> interner;

    InternerFunction(Interner<E> interner) {

    assertThat(pool.intern(canonical)).isSameInstanceAs(canonical);
    assertThat(pool.intern(not)).isSameInstanceAs(canonical);
  }

  public void testWeak_null() {
    Interner<String> pool = Interners.newWeakInterner();
    assertThrows(NullPointerException.class, () -> pool.intern(null));
  }

  public void testWeak_builder() {
    int concurrencyLevel = 42;
    Interner<Object> interner =

    assertThat(pool.intern(canonical)).isSameInstanceAs(canonical);
    assertThat(pool.intern(not)).isSameInstanceAs(canonical);
  }

  public void testWeak_null() {
    Interner<String> pool = Interners.newWeakInterner();
    assertThrows(NullPointerException.class, () -> pool.intern(null));
  }

  public void testWeak_builder() {
    int concurrencyLevel = 42;
    Interner<Object> interner =

    WeakInternerImpl {
      @Override
      public <E> Interner<E> create(Collection<E> contents) {
        Interner<E> interner = Interners.newWeakInterner();
        for (E e : contents) {
          E unused = interner.intern(e);
        }
        return interner;
      }
    },
    StrongInternerImpl {
      @Override
      public <E> Interner<E> create(Collection<E> contents) {

    WeakInternerImpl {
      @Override
      public <E> Interner<E> create(Collection<E> contents) {
        Interner<E> interner = Interners.newWeakInterner();
        for (E e : contents) {
          E unused = interner.intern(e);
        }
        return interner;
      }
    },
    StrongInternerImpl {
      @Override
      public <E> Interner<E> create(Collection<E> contents) {

import com.google.common.annotations.J2ktIncompatible;
import java.time.Duration;

/** This class is for {@code com.google.common.collect} use only! */
@J2ktIncompatible
@GwtIncompatible // java.time.Duration
final class Internal {

  /**
   * Returns the number of nanoseconds of the given duration without throwing or overflowing.
   *
   * <p>Instead of throwing {@link ArithmeticException}, this method silently saturates to either