// not as the type of a variable.
type comparable interface{ comparable }

// iota is a predeclared identifier representing the untyped integer ordinal
// number of the current const specification in a (usually parenthesized)
// const declaration. It is zero-indexed.
const iota = 0 // Untyped int.

// nil is a predeclared identifier representing the zero value for a
// pointer, channel, func, interface, map, or slice type.

We can do better...

## What makes a dependency { #what-makes-a-dependency }

Up to now you have seen dependencies declared as functions.

But that's not the only way to declare dependencies (although it would probably be the more common).

The key factor is that a dependency should be a "callable".

A "**callable**" in Python is anything that Python can "call" like a function.

erations }

Later, when reading about how to structure bigger applications ([Bigger Applications - Multiple Files](../../tutorial/bigger-applications.md){.internal-link target=_blank}), possibly with multiple files, you will learn how to declare a single `dependencies` parameter for a group of *path operations*....

# WebSockets

When defining WebSockets, you normally declare a parameter of type `WebSocket` and with it you can read data from the client and send data to it.

It is provided directly by Starlette, but you can import it from `fastapi`:

```python
from fastapi import WebSocket
```

/// tip

Hug inspired parts of APIStar, and was one of the tools I found most promising, alongside APIStar.

Hug helped inspiring **FastAPI** to use Python type hints to declare parameters, and to generate a schema defining the API automatically.

Hug inspired **FastAPI** to declare a `response` parameter in functions to set headers and cookies.

///

Certifique-se de [Atualizar a versão do FastAPI](../deployment/versions.md#upgrading-the-fastapi-versions){.internal-link target=_blank} para pelo menos 0.95.1 antes de usar `Annotated`.

///

## Declare metadados { #declare-metadata }

Você pode declarar todos os mesmos parâmetros que em `Query`.

Por exemplo, para declarar um valor de metadado `title` para o parâmetro de path `item_id` você pode digitar:

/**
 * Runtime exception wrapper for ServletException.
 *
 * This exception is used to wrap checked ServletExceptions and convert them
 * into unchecked RuntimeExceptions, allowing them to be thrown from methods
 * that don't declare ServletException in their throws clause.
 */
public class ServletRuntimeException extends RuntimeException {

    /** Serial version UID for serialization compatibility. */
    private static final long serialVersionUID = 1L;

# `Response` class

You can declare a parameter in a *path operation function* or dependency to be of type `Response` and then you can set data for the response like headers or cookies.

You can also use it directly to create an instance of it and return it from your *path operations*.

You can import it directly from `fastapi`:

```python
from fastapi import Response
```

///

## Rendre ce paramètre requis

Quand on ne déclare ni validation, ni métadonnée, on peut rendre le paramètre `q` requis en ne lui déclarant juste aucune valeur par défaut :

```Python
q: str
```

à la place de :

```Python
q: Union[str, None] = None
```

Mais maintenant, on déclare `q` avec `Query`, comme ceci :

```Python

   * IOException}, {@code RuntimeException} or {@code Error}. Otherwise, it will be rethrown wrapped
   * in a {@code RuntimeException}. <b>Note:</b> Be sure to declare all of the checked exception
   * types your try block can throw when calling an overload of this method so as to avoid losing
   * the original exception type.
   *