/*
   * Ideally, this class would have exposed only constructors that require a non-null cause. See
   * https://github.com/jspecify/jspecify-reference-checker/blob/61aafa4ae52594830cfc2d61c8b113009dbdb045/src/main/java/com/google/jspecify/nullness/NullSpecTransfer.java#L789
   * and https://github.com/jspecify/jspecify/issues/490.
   *
   * (Perhaps it should also have required that its cause was a RuntimeException. However, that

To see all the options you have, checkout the docs for <a href="https://docs.pydantic.dev/latest/concepts/types/" class="external-link" target="_blank">Pydantic's exotic types</a>. You will see some examples in the next chapter.

For example, as in the `Image` model we have a `url` field, we can declare it to be an instance of Pydantic's `HttpUrl` instead of a `str`:

  /*
   * Ideally, this class would have exposed only constructors that require a non-null cause. See
   * https://github.com/jspecify/jspecify-reference-checker/blob/61aafa4ae52594830cfc2d61c8b113009dbdb045/src/main/java/com/google/jspecify/nullness/NullSpecTransfer.java#L789
   * and https://github.com/jspecify/jspecify/issues/490.
   *
   * (That would also have ensured that its cause was always an Error, rather than possibly another

In this case, you could want to document how that external API *should* look like. What *path operation* it should have, what body it should expect, what response it should return, etc.

## An app with callbacks

Let's see all this with an example.

Imagine you develop an app that allows creating invoices.

These invoices will have an `id`, `title` (optional), `customer`, and `total`.

    {!> ../../../docs_src/dependencies/tutorial008.py!}
    ```

The same way, you could have some dependencies with `yield` and some other dependencies with `return`, and have some of those depend on some of the others.

And you could have a single dependency that requires several other dependencies with `yield`, etc.

You can have any combinations of dependencies that you want.

	// If we have have any records left, return these before any error.
	for len(r.current) <= r.recordsRead {
		if r.err != nil {
			return nil, r.err
		}
		// Move to next block
		item, ok := <-r.queue
		if !ok {
			r.err = io.EOF
			return nil, r.err
		}
		//nolint:staticcheck // SA6002 Using pointer would allocate more since we would have to copy slice header before taking a pointer.

  * In practice, this largely means that references are fully qualified in the API. IP Addresses (generally) have a network associated with them, node names have a cluster associated with them, etc.

See the [XDS Evolution](https://docs.google.com/document/d/1V5wkeBHbLSLMzAMbwFlFZNHdZPyUEspG4lHbnB0UaCg/edit) document for more history and details.

In this case, it would be better to get **one extra server** and run some processes on it so that they all have **enough RAM and CPU time**.

There's also the chance that for some reason you have a **spike** of usage of your API. Maybe it went viral, or maybe some other services or bots start using it. And you might want to have extra resources to be safe in those cases.

                available, instead of erroring out, the dependency result will be
                `None`.

                This is useful when you want to have optional authentication.

                It is also useful when you want to have authentication that can be
                provided in one of multiple optional ways (for example, in a query
                parameter or in an HTTP Bearer token).
                """

    like:

    ```
    Authorization: Bearer deadbeef12346
    ```

    In this case:

    * `scheme` will have the value `"Bearer"`
    * `credentials` will have the value `"deadbeef12346"`
    """

    scheme: Annotated[
        str,
        Doc(
            """
            The HTTP authorization scheme extracted from the header value.