* future version of {@code com.google.common.base.Supplier} will be made to <i>extend</i> {@code
 * java.util.function.Supplier}, making conversion code necessary only in one direction. At that
 * time, this interface will be officially discouraged.
 *
 * @author Harry Heymann
 * @since 2.0
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault

      this.supplier = supplier;
    }
  }

  @Param private CollectionType source;

  enum Operation {
    FIND_FIRST {
      @Override
      Object operate(Stream<?> stream) {
        return stream.findFirst();
      }
    },
    STREAMS_ONLY_ELEMENT {
      @Override
      Object operate(Stream<?> stream) {
        try {
          return stream.collect(onlyElement());

     *
     * @param error the error that caused this log
     */
    void debug(Throwable error);

    void debug(Supplier<String> content);

    void debug(Supplier<String> content, Throwable error);

    /**
     * {@return true if the <b>info</b> error level is enabled}
     */
    boolean isInfoEnabled();

    /**

    @Override
    public void debug(Throwable error) {
        logger.debug("", error);
    }

    @Override
    public void debug(Supplier<String> content) {
        if (isDebugEnabled()) {
            logger.debug(content.get());
        }
    }

    @Override
    public void debug(Supplier<String> content, Throwable error) {
        if (isDebugEnabled()) {
            logger.debug(content.get(), error);
        }
    }

    protected StringBuilder append(final StringBuilder buf, final String key, final Supplier<Object> supplier) {
        final StringBuilder tempBuf = new StringBuilder();
        tempBuf.append('"').append(key).append("\":");
        try {
            final Object value = supplier.get();
            if (value == null) {
                tempBuf.append("null");

   *
   * @param callable The callable to wrap
   * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once
   *     for each invocation of the wrapped callable.
   */
  @J2ktIncompatible
  @GwtIncompatible // threads
  static <T extends @Nullable Object> Callable<T> threadRenaming(
      Callable<T> callable, Supplier<String> nameSupplier) {
    checkNotNull(nameSupplier);
    checkNotNull(callable);

    @Nullable Object get() throws Throwable;
  }

  @CanIgnoreReturnValue
  static <T extends Throwable> T assertThrows(
      Class<T> expectedThrowable, ThrowingSupplier supplier) {
    return doAssertThrows(expectedThrowable, supplier, /* userPassedSupplier= */ true);
  }

  @CanIgnoreReturnValue
  static <T extends Throwable> T assertThrows(
      Class<T> expectedThrowable, ThrowingRunnable runnable) {

    @Nullable Object get() throws Throwable;
  }

  @CanIgnoreReturnValue
  static <T extends Throwable> T assertThrows(
      Class<T> expectedThrowable, ThrowingSupplier supplier) {
    return doAssertThrows(expectedThrowable, supplier, /* userPassedSupplier= */ true);
  }

  @CanIgnoreReturnValue
  static <T extends Throwable> T assertThrows(
      Class<T> expectedThrowable, ThrowingRunnable runnable) {

                }
            }
            return model;
        }

        public Model computeIfAbsent(Supplier<Model> supplier) {
            if (!set) {
                synchronized (this) {
                    if (!set) {
                        this.set = true;
                        this.model = supplier.get();
                        this.notifyAll();
                    }
                }
            }

  }

  private static void assertChecksum(ImmutableSupplier<Checksum> supplier, String input) {
    byte[] bytes = HashTestUtils.ascii(input);

    Checksum checksum = supplier.get();
    checksum.update(bytes, 0, bytes.length);
    long value = checksum.getValue();

    String toString = "name";
    HashFunction func = new ChecksumHashFunction(supplier, 32, toString);
    assertEquals(toString, func.toString());