trying to box her own ears for having cheated herself in a game
of croquet she was playing against herself, for this curious
child was very fond of pretending to be two people.  `But it's no
use now,' thought poor Alice, `to pretend to be two people!  Why,
there's hardly enough of me left to make ONE respectable
person!'

  Soon her eye fell on a little glass box that was lying under
the table:  she opened it, and found in it a very small cake, on

 * of the <i>next</i> request. I.e., if an expensive task arrives at an idle RateLimiter, it will be
 * granted immediately, but it is the <i>next</i> request that will experience extra throttling,
 * thus paying for the cost of the expensive task.
 *
 * @author Dimitris Andreou
 * @since 13.0
 */
// TODO(user): switch to nano precision. A natural unit of cost is "bytes", and a micro precision

   *
   * <p>The expected (but not guaranteed) performance of the special implementation differs from
   * {@code getStackTrace} in one main way: The {@code lazyStackTrace} call itself returns quickly
   * by delaying the per-stack-frame work until each element is accessed. Roughly speaking:
   *
   * <ul>
   *   <li>{@code getStackTrace} takes {@code stackSize} time to return but then negligible time to

   *
   * <p>The expected (but not guaranteed) performance of the special implementation differs from
   * {@code getStackTrace} in one main way: The {@code lazyStackTrace} call itself returns quickly
   * by delaying the per-stack-frame work until each element is accessed. Roughly speaking:
   *
   * <ul>
   *   <li>{@code getStackTrace} takes {@code stackSize} time to return but then negligible time to

@GwtCompatible
@ElementTypesAreNonnullByDefault
final class NullnessCasts {
  /**
   * Accepts a {@code @Nullable T} and returns a plain {@code T}, without performing any check that
   * that conversion is safe.
   *
   * <p>This method is intended to help with usages of type parameters that have {@linkplain

 * can't get by with the standard implementations, prefer to derive a new {@code Future} instance
 * with the methods in {@link Futures} or, if necessary, to extend {@link AbstractFuture}.
 *
 * <p>Occasionally, an API will return a plain {@code Future} and it will be impossible to change
 * the return type. For this case, we provide a more expensive workaround in {@code
 * JdkFutureAdapters}. However, when possible, it is more efficient and reliable to create a {@code

   * only contain entries which are already present in the cache.
   *
   * @since 11.0
   */
  /*
   * <? extends Object> is mostly the same as <?> to plain Java. But to nullness checkers, they
   * differ: <? extends Object> means "non-null types," while <?> means "all types."
   */
  ImmutableMap<K, V> getAllPresent(Iterable<? extends Object> keys);

  /**

   * returns. This method may be useful when testing the garbage collection mechanism itself, or
   * inhibiting a spontaneous GC initiation in subsequent code.
   *
   * <p>In contrast, a plain call to {@link java.lang.System#gc()} does not ensure finalization
   * processing and may run concurrently, for example, if the JVM flag {@code
   * -XX:+ExplicitGCInvokesConcurrent} is used.
   *

       *
       * (And I don't believe there's any situation in which we call x.combine(y) when x is a plain
       * ImmutableSet.Builder but y is an ImmutableSortedSet.Builder (or vice versa). Certainly
       * ImmutableSortedSet.Builder.combine() is written as if its argument will never be a plain
       * ImmutableSet.Builder: It casts immediately to ImmutableSortedSet.Builder.)
       */
      copyIfNecessary();

 *       considered "compiled comments."
 *   <li>An explicit {@code if/throw} (as illustrated below) is always acceptable; we still
 *       recommend using our {@link VerifyException} exception type. Throwing a plain {@link
 *       RuntimeException} is frowned upon.
 *   <li>Use of {@link java.util.Objects#requireNonNull(Object)} is generally discouraged, since