Se você declarar o tipo de retorno, o FastAPI o usará para **validar** os dados, **documentá-los** no OpenAPI, **filtrá-los** e **serializá-los** usando o Pydantic.

/// tip | Dica

Como o Pydantic fará a serialização no lado em **Rust**, você terá uma **performance** muito maior do que se não declarar um tipo de retorno.

///

### Funções de operação de rota não assíncronas { #non-async-path-operation-functions }

 * directly; please see {@link com.google.common.collect.testing.CollectionTestSuiteBuilder}.
 *
 * @author Kevin Bourrillion
 * @author Chris Povirk
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.
@SuppressWarnings("JUnit4ClassUsedInJUnit3")

import org.jspecify.annotations.Nullable;

/**
 * Basic implementation of {@code Multiset<E>} backed by an instance of {@code
 * ObjectCountHashMap<E>}.
 *
 * <p>For serialization to work, the subclass must specify explicit {@code readObject} and {@code
 * writeObject} methods.
 *
 * @author Kevin Bourrillion
 */
@GwtCompatible
abstract class AbstractMapBasedMultiset<E extends @Nullable Object> extends AbstractMultiset<E>

        assertTrue(it.hasNext());
        assertEquals("ok/", it.next().getName());
        assertFalse(it.hasNext());

        // When filter is used, it must not be called for the invalid entry
        if (useFilter) {
            verify(filter, times(1)).accept(any());
        }
    }

    @Test

如果你把回傳型別宣告為 `AsyncIterable[Item]`，FastAPI 會用它來透過 Pydantic 進行**驗證**、**文件化**與**序列化**。

{* ../../docs_src/server_sent_events/tutorial001_py310.py ln[1:25] hl[10:12,23] *}

/// tip

因為 Pydantic 會在 **Rust** 端進行序列化，如果你有宣告回傳型別，效能會比未宣告時高很多。

///

### 非 async 的路徑操作函式 { #non-async-path-operation-functions }

你也可以使用一般的 `def` 函式（沒有 `async`），並同樣使用 `yield`。

FastAPI 會確保正確執行，不會阻塞事件迴圈。

        } else if (!(USER_LEVEL.equals(sourceLevel) || PROJECT_LEVEL.equals(sourceLevel)  || GLOBAL_LEVEL.equals(sourceLevel))) {
            throw new IllegalArgumentException("sourceLevel must be one of: {" + USER_LEVEL + "," + PROJECT_LEVEL + "," + GLOBAL_LEVEL + "}");
        } else {
            this.sourceLevel = sourceLevel;
            this.sourceLevelSet = true;
        }
    }

   */
  protected abstract Iterable<? extends Stimulus<E, ? super I>> getStimulusValues();

  /**
   * Returns a new target iterator each time it's called. This is the iterator you are trying to
   * test. This must return an Iterator that returns the expected elements passed to the constructor
   * in the given order. Warning: it is not enough to simply pull multiple iterators from the same

/**
 * Base class for implementing services that can handle {@link #doStart} and {@link #doStop}
 * requests, responding to them with {@link #notifyStarted()} and {@link #notifyStopped()}
 * callbacks. Its subclasses must manage threads manually; consider {@link
 * AbstractExecutionThreadService} if you need only a single execution thread.
 *
 * @author Jesse Wilson
 * @author Luke Sandberg
 * @since 1.0
 */
@GwtIncompatible

    the OkHttp version in custom `User-Agent` headers.

 *  Fix: Don't crash when running as a plugin in Android Studio Canary 4.1. To enable
    platform-specific TLS features OkHttp must detect whether it's running in a JVM or in Android.
    The upcoming Android Studio runs in a JVM but has classes from Android and that confused OkHttp!

    }
    return result;
  }

  private static int checkNoOverflow(long result) {
    checkArgument(
        result == (int) result,
        "the total number of elements (%s) in the arrays must fit in an int",
        result);
    return (int) result;
  }

  /**
   * Returns an array containing the same values as {@code array}, but guaranteed to be of a