*
 * <p><b>Note:</b> by default, the returned cache uses equality comparisons (the {@link
 * Object#equals equals} method) to determine equality for keys or values. However, if {@link
 * #weakKeys} was specified, the cache uses identity ({@code ==}) comparisons instead for keys.
 * Likewise, if {@link #weakValues} or {@link #softValues} was specified, the cache uses identity
 * comparisons for values.
 *

    a bug where a shared connection pool did not guarantee shared connections in some cases.
 *  Fix: Prefer the server's response body on all conditional cache misses. Previously we would
    return the cached response's body if it had a newer `Last-Modified` date.
 *  Fix: Update the stored timestamp on conditional cache hits.

   * href="https://docs.oracle.com/javase/tutorial/java/generics/genTypeInference.html#type-inference-instantiation">"diamond"
   * syntax</a>. One caveat to this is that the {@code TreeSet} constructor uses a null {@code
   * Comparator} to mean "natural ordering," whereas this factory rejects null. Clean your code
   * accordingly.
   *
   * @param comparator the comparator to use to sort the set

     *   failure to reach any individual IP address doesn't fail the overall request. This can
     *   increase availability of multi-homed services.
     *
     * * **Stale pooled connections.** The [ConnectionPool] reuses sockets
     *   to decrease request latency, but these connections will occasionally time out.
     *
     * * **Unreachable proxy servers.** A [ProxySelector] can be used to

   * penalty of applying the batches is spread across threads so that the amortized cost is slightly
   * higher than performing just the operation without enforcing the capacity constraint.
   *
   * This implementation uses a per-segment queue to record a memento of the additions, removals,
   * and accesses that were performed on the map. The queue is drained on writes and when it exceeds
   * its capacity threshold.
   *

    val snapshot = cache["b"]!!
    snapshot.close()
    assertThat(cache.edit("d")).isNull()
    assertThat(taskFaker.isIdle()).isFalse()

    // On cache misses, no retry job is queued.
    assertThat(cache["c"]).isNull()
    assertThat(taskFaker.isIdle()).isFalse()

    // Let the rebuild complete successfully.

    assertThat(server.takeRequest().exchangeIndex).isEqualTo(1) // Pooled connection.
    assertThat(server.takeRequest().exchangeIndex).isEqualTo(0) // New connection.

    // Third call reuses the second connection.
    val response3 = client.newCall(request).execute()
    assertThat(response3.body.string()).isEqualTo("def")
    assertThat(server.takeRequest().exchangeIndex).isEqualTo(1) // New connection.
  }

 * (The same goes for the message-accepting overloads.)
 *
 * <h3>Only {@code %s} is supported</h3>
 *
 * <p>{@code Preconditions} uses {@link Strings#lenientFormat} to format error message template
 * strings. This only supports the {@code "%s"} specifier, not the full range of {@link