# 类作为依赖项 { #classes-as-dependencies }

在深入探究 **依赖注入** 系统之前，让我们升级之前的例子。

## 来自前一个例子的`dict` { #a-dict-from-the-previous-example }

在前面的例子中, 我们从依赖项 ("可依赖对象") 中返回了一个 `dict`:

{* ../../docs_src/dependencies/tutorial001_an_py310.py hl[9] *}

但是后面我们在路径操作函数的参数 `commons` 中得到了一个 `dict`。

我们知道编辑器不能为 `dict` 提供很多支持(比如补全)，因为编辑器不知道 `dict` 的键和值类型。

对此，我们可以做的更好...

## 什么构成了依赖项 { #what-makes-a-dependency }

到目前为止，你看到的依赖项都被声明为函数。

Al igual que al declarar parámetros de query, cuando un atributo del modelo tiene un valor por defecto, no es obligatorio. De lo contrario, es obligatorio. Usa `None` para hacerlo solo opcional.

Por ejemplo, el modelo anterior declara un “`object`” JSON (o `dict` en Python) como:

```JSON
{
    "name": "Foo",
    "description": "An optional description",
    "price": 45.2,
    "tax": 3.5
}
```

 * given at creation time, the natural order of elements is used. If no maximum size is given at
 * creation time, the queue is unbounded.
 *
 * <p>Usage example:
 *
 * {@snippet :
 * MinMaxPriorityQueue<User> users = MinMaxPriorityQueue.orderedBy(userComparator)
 *     .maximumSize(1000)
 *     .create();
 * }
 *

 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p><b>Warning:</b> The methods of {@code ForwardingNavigableSet} forward <i>indiscriminately</i>
 * to the methods of the delegate. For example, overriding {@link #add} alone <i>will not</i> change
 * the behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you should

 *       in any other way than how {@code Stopwatch} uses them.
 *   <li>An alternative source of nanosecond ticks can be substituted, for example for testing or
 *       performance reasons, without affecting most of your code.
 * </ul>
 *
 * <p>The one downside of {@code Stopwatch} relative to {@link System#nanoTime()} is that {@code

 * more ACEs are evaluated until all desired access bits (combined)
 * are "allowed". If all of the desired access bits are not "allowed"
 * the then same process is repeated for inherited ACEs.
 * <p>
 * For example, if user <code>WNET\alice</code> tries to open a file
 * with desired access bits <code>0x00000003</code> (<code>FILE_READ_DATA |
 * FILE_WRITE_DATA</code>) and the target file has the following security
 * descriptor ACEs:

        long time = SMBUtil.readTime(src, 0);
        assertEquals(-SmbConstants.MILLISECONDS_BETWEEN_1970_AND_1601, time);

        // Test with specific time value
        long testTime = 131768928000000000L; // Example Windows file time
        SMBUtil.writeInt8(testTime, src, 8);
        long readTime = SMBUtil.readTime(src, 8);
        assertEquals((testTime / 10000L - SmbConstants.MILLISECONDS_BETWEEN_1970_AND_1601), readTime);
    }

// path when needed, in order to avoid the default 260 character file
// path limit imposed by Windows. If path is not easily converted to
// the extended-length form (for example, if path is a relative path
// or contains .. elements), or is short enough, fixLongPath returns
// path unmodified.
//
// See https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx#maxpath

   */
  @Test
  fun customTrailersDoNotUseResponseBody() {
    val response =
      Response
        .Builder()
        .request(Request(url = "https://example.com".toHttpUrl()))
        .protocol(Protocol.HTTP_1_1)
        .code(200)
        .message("OK")
        .body(
          object : ResponseBody() {
            override fun contentType(): MediaType? = null

     * created and what is required of it. The second degree of state is the
     * most common. This is the state information that would be retrieved from
     * WINS for example. Natrually it is not practical for every NbtAddress
     * to be populated will all state requiring a Node Status on every host
     * encountered. The below methods allow state to be populated when requested