## 在嵌套数据结构中使用数据类

您还可以把 `dataclasses` 与其它类型注解组合在一起，创建嵌套数据结构。

还有一些情况也可以使用 Pydantic 的 `dataclasses`。例如，在 API 文档中显示错误。

本例把标准的 `dataclasses` 直接替换为 `pydantic.dataclasses`：

```{ .python .annotate hl_lines="1  5  8-11  14-17  23-25  28" }
{!../../docs_src/dataclasses/tutorial003.py!}
```

1. 本例依然要从标准的 `dataclasses` 中导入 `field`；

2. 使用 `pydantic.dataclasses` 直接替换 `dataclasses`；

import static java.lang.annotation.RetentionPolicy.RUNTIME;

import com.google.common.annotations.GwtCompatible;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * Annotates a "top-level" type-variable usage that takes its nullness from the type argument
 * supplied by the user of the class. For example, {@code Multiset.Entry.getElement()} returns
 * {@code @ParametricNullness E}, which means:
 *

import static java.lang.annotation.RetentionPolicy.RUNTIME;

import com.google.common.annotations.GwtCompatible;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * Annotates a "top-level" type-variable usage that takes its nullness from the type argument
 * supplied by the user of the class. For example, {@code Multiset.Entry.getElement()} returns
 * {@code @ParametricNullness E}, which means:
 *

import static java.lang.annotation.RetentionPolicy.RUNTIME;

import com.google.common.annotations.GwtCompatible;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * Annotates a "top-level" type-variable usage that takes its nullness from the type argument
 * supplied by the user of the class. For example, {@code Multiset.Entry.getElement()} returns
 * {@code @ParametricNullness E}, which means:
 *

import static java.lang.annotation.RetentionPolicy.RUNTIME;

import com.google.common.annotations.GwtCompatible;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * Annotates a "top-level" type-variable usage that takes its nullness from the type argument
 * supplied by the user of the class. For example, {@code Multiset.Entry.getElement()} returns
 * {@code @ParametricNullness E}, which means:
 *

import static java.lang.annotation.RetentionPolicy.RUNTIME;

import com.google.common.annotations.GwtCompatible;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * Annotates a "top-level" type-variable usage that takes its nullness from the type argument
 * supplied by the user of the class. For example, {@code Multiset.Entry.getElement()} returns
 * {@code @ParametricNullness E}, which means:
 *

import static java.lang.annotation.RetentionPolicy.RUNTIME;

import com.google.common.annotations.GwtCompatible;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * Annotates a "top-level" type-variable usage that takes its nullness from the type argument
 * supplied by the user of the class. For example, {@code Multiset.Entry.getElement()} returns
 * {@code @ParametricNullness E}, which means:
 *

In diesem Fall können Sie einfach die Standard-`dataclasses` durch `pydantic.dataclasses` ersetzen, was einen direkten Ersatz darstellt:

```{ .python .annotate hl_lines="1  5  8-11  14-17  23-25  28" }
{!../../docs_src/dataclasses/tutorial003.py!}
```

1. Wir importieren `field` weiterhin von Standard-`dataclasses`.

    }
  }
}

project.applyOsgi(
  "Export-Package: okhttp3,okhttp3.internal.*;okhttpinternal=true;mandatory:=okhttpinternal",
  "Import-Package: " +
    "android.*;resolution:=optional," +
    "com.oracle.svm.core.annotate;resolution:=optional," +
    "com.oracle.svm.core.configure;resolution:=optional," +
    "dalvik.system;resolution:=optional," +
    "org.conscrypt;resolution:=optional," +
    "org.bouncycastle.*;resolution:=optional," +

In an expression switch, the cases contain expressions that are compared
against the value of the switch expression.
In a type switch, the cases contain types that are compared against the
type of a specially annotated switch expression.
The switch expression is evaluated exactly once in a switch statement.
</p>

<h4 id="Expression_switches">Expression switches</h4>

<p>
In an expression switch,