/// note | Technical Details

When you import `Query`, `Path` and others from `fastapi`, they are actually functions.

That when called, return instances of classes of the same name.

So, you import `Query`, which is a function. And when you call it, it returns an instance of a class also named `Query`.

These functions are there (instead of just using the classes directly) so that your editor doesn't mark errors about their types.

  @Override
  public Set<T> asSet() {
    return Collections.singleton(reference);
  }

  @Override
  public <V> Optional<V> transform(Function<? super T, V> function) {
    return new Present<>(
        checkNotNull(
            function.apply(reference),
            "the Function passed to Optional.transform() must not return null."));
  }

  @Override
  public boolean equals(@Nullable Object obj) {

        </ul>
        <script>
        var ws = null;
            function connect(event) {
                var itemId = document.getElementById("itemId")
                var token = document.getElementById("token")
                ws = new WebSocket("ws://localhost:8000/items/" + itemId.value + "/ws?token=" + token.value);
                ws.onmessage = function(event) {
                    var messages = document.getElementById('messages')

### Custom Generate Unique ID Function { #custom-generate-unique-id-function }

FastAPI uses a **unique ID** for each *path operation*, which is used for the **operation ID** and also for the names of any needed custom models, for requests or responses.

You can customize that function. It takes an `APIRoute` and outputs a string.

# Background Tasks - `BackgroundTasks`

You can declare a parameter in a *path operation function* or dependency function with the type `BackgroundTasks`, and then you can use it to schedule the execution of background tasks after the response is sent.

You can import it directly from `fastapi`:

```python
from fastapi import BackgroundTasks
```

      return delegate;
    }
  }

  private static String encode(String str) {
    return BaseEncoding.base64().encode(str.getBytes(UTF_8));
  }

  private static final Function<String, String> DECODE_FUNCTION =
      new Function<String, String>() {
        @Override
        public String apply(String input) {
          return new String(BaseEncoding.base64().decode(input), UTF_8);
        }
      };

      }
    }
  }

  /**
   * Returns a function that delegates to the {@link Interner#intern} method of the given interner.
   *
   * @since 8.0
   */
  public static <E> Function<E, E> asFunction(Interner<E> interner) {
    return new InternerFunction<>(checkNotNull(interner));
  }

  private static final class InternerFunction<E> implements Function<E, E> {

    private final Interner<E> interner;

  private static <T> void testSuccessfulForwarding(
      Class<T> interfaceType, Method method, Function<? super T, ? extends T> wrapperFunction) {
    new InteractionTester<T>(interfaceType, method).testInteraction(wrapperFunction);
  }

  private static <T> void testExceptionPropagation(
      Class<T> interfaceType, Method method, Function<? super T, ? extends T> wrapperFunction) {
    RuntimeException exception = new RuntimeException();

// or a function call.
type PrimaryTerm struct {
	Value         *LitValue   `parser:"  @@"`
	JPathExpr     *JSONPath   `parser:"| @@"`
	ListExpr      *ListExpr   `parser:"| @@"`
	SubExpression *Expression `parser:"| \"(\" @@ \")\""`
	// Include function expressions here.
	FuncCall *FuncExpr `parser:"| @@"`
}

// FuncExpr represents a function call
type FuncExpr struct {

        </ul>
        <script>
        var ws = null;
            function connect(event) {
                var itemId = document.getElementById("itemId")
                var token = document.getElementById("token")
                ws = new WebSocket("ws://localhost:8000/items/" + itemId.value + "/ws?token=" + token.value);
                ws.onmessage = function(event) {
                    var messages = document.getElementById('messages')