# Using Dataclasses

FastAPI is built on top of **Pydantic**, and I have been showing you how to use Pydantic models to declare requests and responses.

But FastAPI also supports using <a href="https://docs.python.org/3/library/dataclasses.html" class="external-link" target="_blank">`dataclasses`</a> the same way:

{* ../../docs_src/dataclasses/tutorial001.py hl[1,7:12,19:20] *}

### Expiry or removal events

            try {
              plan.connectTcp()
            } catch (e: Throwable) {
              ConnectResult(plan, throwable = e)
            }
          // Only post a result if this hasn't since been canceled.
          if (plan in tcpConnectsInFlight) {
            connectResults.put(connectResult)
          }
          return -1L
        }
      },
    )
    return null
  }

       changes with every test execution, such that running the test
       actually changes the test classpath itself. This means that it
       can"t benefit from incremental build acceleration, because on every
       execution it sees that the classpath has changed, and so to be
       safe, it needs to re-run.

       - This is unfortunate, because actually it would be safe to declare
       the task as up-to-date, because these two files, which are based on

  @Param boolean noWorkToDo;

  Random random;
  String testString;

  @BeforeExperiment
  void setUp() {
    random = new Random(0xdeadbeef); // fix the seed so results are comparable across runs

    int nonAlpha = size / nonAlphaRatio;
    int alpha = size - nonAlpha;

    List<Character> chars = Lists.newArrayListWithCapacity(size);
    for (int i = 0; i < alpha; i++) {

 * @author James Sexton
 */
@ElementTypesAreNonnullByDefault
class MapIteratorCache<K, V> {
  private final Map<K, V> backingMap;

  /*
   * Per JDK: "the behavior of a map entry is undefined if the backing map has been modified after
   * the entry was returned by the iterator, except through the setValue operation on the map entry"
   * As such, this field must be cleared before every map mutation.
   *

modified object code on the User Product (for example, the work has
been installed in ROM).

  The requirement to provide Installation Information does not include a
requirement to continue to provide support service, warranty, or updates
for a work that has been modified or installed by the recipient, or for
the User Product in which it has been modified or installed.  Access to a

        .build();
    ```

 *  New: You can now access HTTP trailers with `Response.trailers()`. This method may only be called
    after the entire HTTP response body has been read.

 *  New: Upgrade to Okio 1.17.3. If you're on Kotlin-friendly Okio 2.x this release requires 2.2.2
    or newer.

    ```kotlin
    implementation("com.squareup.okio:okio:1.17.3")
    ```

 * address. These name resolution mechanisms and their resolution order
 * can be changed (See <a href="../../../resolver.html">Setting Name
 * Resolution Properties</a>). The servername and path components are
 * not case sensitive but the domain, username, and password components
 * are. It is also likely that properties must be specified for jcifs
 * to function (See <a href="../../overview-summary.html#scp">Setting

	}

	eventData, eErr := target.store.Get(key)
	if eErr != nil {
		// The last event key in a successful batch will be sent in the channel atmost once by the replayEvents()
		// Such events will not exist and wouldve been already been sent successfully.
		if os.IsNotExist(eErr) {
			return nil
		}
		return eErr
	}

	if err := target.send(eventData); err != nil {
		return err
	}

	return target.store.Del(key)
}