translated concept-autoloading.md [skip ci]

docs/guide-zh-CN/concept-autoloading.md

 类自动加载（Autoloading）
 =================
 
-Yii relies on the [class autoloading mechanism](http://www.php.net/manual/en/language.oop5.autoload.php)
-to locate and include required class files. It provides a high-performance class autoloader that is compliant to the
-[PSR-4 标准](https://github.com/php-fig/fig-standards/blob/master/proposed/psr-4-autoloader/psr-4-autoloader.md).
-The autoloader is installed when you include the `Yii.php` file.
+Yii 依靠[类自动加载机制(http://www.php.net/manual/en/language.oop5.autoload.php)来定位和包含所需的类文件。它提供一个高性能且完美支持[PSR-4 标准](https://github.com/php-fig/fig-standards/blob/master/proposed/psr-4-autoloader/psr-4-autoloader.md)（[中文汉化](https://github.com/hfcorriez/fig-standards/blob/zh_CN/%E6%8E%A5%E5%8F%97/PSR-4-autoloader.md)）的自动加载器。该自动加载器会在包含 `Yii.php` 文件时安装好。
 
-> Note: For simplicity of description, in this section we will only talk about autoloading of classes. However, keep in
-  mind that the content we are describing here applies to autoloading of interfaces and traits as well.
+> 注意：为了简化叙述，本篇文档中我们只会提及类的自动加载。不过，要记得文中的描述同样也适用于接口和Trait（特质）的自动加载哦。
 
 
 使用 Yii 自动加载器 <a name="using-yii-autoloader"></a>
 ------------------------
 
-To make use of the Yii class autoloader, you should follow two simple rules when creating and naming your classes:
+要使用 Yii  的类自动加载器，你需要在创建和命名尼德类的时候遵循两个简单的规则：
 
-* Each class must be under some namespace (e.g. `foo\bar\MyClass`).
-* Each class must be saved in an individual file whose path is determined by the following algorithm:
+* 每个类都必须置于命名空间之下 (比如 `foo\bar\MyClass`)。
+* 每个类都必须保存为单独文件，且其完整路径能用以下算法取得：
 
 ```php
-// $className is a fully qualified class name with the leading backslash
+// $className 是一个开头包含反斜杠的完整类名（译者注：请自行谷歌：fully qualified class name）
 $classFile = Yii::getAlias('@' . str_replace('\\', '/', $className) . '.php');
 ```
 
-For example, if a class name is `foo\bar\MyClass`, the [alias](concept-aliases.md) for the corresponding class file path
-would be `@foo/bar/MyClass.php`. In order for this alias to be able to be resolved into a file path,
-either `@foo` or `@foo/bar` must be a [root alias](concept-aliases.md#defining-aliases).
+举例来说，若某个类名为 `foo\bar\MyClass`，对应类的文件路径[别名](concept-aliases.md)会是 
+`@foo/bar/MyClass.php`。为了让该别名能被正确解析为文件路径，`@foo` 或 `@foo/bar` 
+中的一个必须是[根别名](concept-aliases.md#defining-aliases)。
 
-When you are using the [Basic Application Template](start-basic.md), you may put your classes under the top-level
-namespace `app` so that they can be autoloaded by Yii without the need of defining a new alias. This is because
-`@app` is a [predefined alias](concept-aliases.md#predefined-aliases), and a class name like `app\components\MyClass`
-can be resolved into the class file `AppBasePath/components/MyClass.php`, according to the algorithm we just described.
+当我们使用[基本应用模版](start-basic.md)时，你可以把你的类放置在顶级命名空间 `app` 下，这样它们就可以被 Yii
+自动加载，而无需定义一个新的别名。这是因为 `@app` 本身是一个[预定义别名](concept-aliases.md#predefined-aliases)，且类似于 `app\components\MyClass` 这样的类名，基于我们刚才所提到的算法，可以正确解析出 `AppBasePath/components/MyClass.php` 路径。
 
-In the [Advanced Application Template](tutorial-advanced-app.md), each tier has its own root alias. For example,
-the front-end tier has a root alias `@frontend` while the back-end tier `@backend`. As a result, you may
-put the front-end classes under the namespace `frontend` while the back-end classes under `backend`. This will
-allow these classes to be autoloaded by the Yii autoloader.
+在[高级应用模版](tutorial-advanced-app.md)里，每一逻辑层级会使用他自己的根别名。比如，在前端层，会使用 `@frontend` 
+而后端层会使用 `@backend`。因此，你可以把前端的类放在 `frontend` 命名空间，而后端的类放在 `backend`。 这样这些类就可以被 Yii 自动加载了。
 
 
 类映射表（Class Map） <a name="class-map"></a>
 ---------
 
-The Yii class autoloader supports the *class map* feature which maps class names to the corresponding class file paths.
-When the autoloader is loading a class, it will first check if the class is found in the map. If so, the corresponding
-file path will be included directly without further check. This makes class autoloading super fast. In fact,
-all core Yii classes are being autoloaded this way.
+Yii 类自动加载器支持 **类映射表** 功能，该功能会建立一个从类的名字到类文件路径的映射。当自动加载器加载一个文件时，他首先检查映射表里有没有该类。如果有，对应的文件路径就直接加载了，省掉了进一步的检查。它可以让类的自动加载变得炒鸡快！事实上，所有的 Yii 核心类都是这样加载的。
 
-You may add a class to the class map `Yii::$classMap` as follows,
+你可以用 `Yii::$classMap` 方法向映射表中添加类，
 
 ```php
 Yii::$classMap['foo\bar\MyClass'] = 'path/to/MyClass.php';
 ```
 
-[Aliases](concept-aliases.md) can be used to specify class file paths. You should set the class map in the
-[bootstrapping](runtime-bootstrapping.md) process so that the map is ready before your classes are used.
+[别名](concept-aliases.md)可以被用于指定类文件的路径。你应该在[引导启动](runtime-bootstrapping.md)的过程中设置类映射表，这样映射表就可以在你使用具体类之前就准备好。
 
 
 用其他自动加载器 <a name="using-other-autoloaders"></a>
 -----------------------
 
-Because Yii embraces Composer as a package dependency manager, it is recommended that you also install
-the Composer autoloader. If you are using some 3rd-party libraries that have their autoloaders, you should
-also install them.
+因为 Yii 完全支持 Composer 成为一个依赖包管理器，所以推荐你也同时安装 Composer 的自动加载器，如果你用了一些自带自动加载器的第三方类库，你应该也安装下它们。
 
-When you are using the Yii autoloader together with other autoloaders, you should include the `Yii.php` file
-*after* all other autoloaders are installed. This will make the Yii autoloader to be the first one responding to
-any class autoloading request. For example, the following code is extracted from
-the [entry script](structure-entry-scripts.md) of the [Basic Application Template](start-basic.md). The first
-line installs the Composer autoloader, while the second line installs the Yii autoloader.
+在你同时使用其他自动加载器和 Yii 自动加载器的时候，你应该在其他自动加载器安装成功 **之后**，再包含`Yii.php` 
+文件。这将使 Yii 成为第一个响应任何类自动加载请求的自动加载器。举例来说，以下代码提取自[基本应用模版](start-basic.md)的[入口脚本](structure-entry-scripts.md) 。第一行安装了 Composer 的自动加载器，第二行才是 Yii 的自动加载器：
 
 ```php
 require(__DIR__ . '/../vendor/autoload.php');
 require(__DIR__ . '/../vendor/yiisoft/yii2/Yii.php');
 ```
 
-You may use the Composer autoloader alone without the Yii autoloader. However, by doing so, the performance
-of your class autoloading may be degraded, and you must follow the rules set by Composer in order for your classes
-to be autoloadable.
+你也可以只使用 Composer 的自动加载，而不用 Yii 的自动加载。不过这样做的话，类的加载效率会下降，且你必须遵循 Composer 所设定的规则，从而让你的类满足可以被自动加载的要求。
 
-> Info: If you do not want to use the Yii autoloader, you must create your own version of the `Yii.php` file
-  and include it in your [entry script](structure-entry-scripts.md).
+> 补充：若你不想要使用 Yii 的自动加载器，你必须创建一个你自己版本的 `Yii.php` 文件，并把它包含进你的[入口脚本](structure-entry-scripts.md)里。
 
 
 自动加载扩展类 <a name="autoloading-extension-classes"></a>
 -----------------------------
 
-The Yii autoloader is capable of autoloading [extension](structure-extensions.md) classes. The sole requirement
-is that an extension specifies the `autoload` section correctly in its `composer.json` file. Please refer to the
-[Composer documentation](https://getcomposer.org/doc/04-schema.md#autoload) for more details about specifying `autoload`.
+Yii 自动加载器支持自动加载[扩展](structure-extensions.md)的类。唯一的要求是它需要在 `composer.json` 
+文件里正确地定义 `autoload` 部分。请参考 [Composer 文档（英文）](https://getcomposer.org/doc/04-schema.md#autoload)（[中文汉化](https://github.com/5-say/composer-doc-cn/blob/master/cn-introduction/04-schema.md#autoload)），来了解如何正确描述 `autoload` 的更多细节。
 
-In case you do not use the Yii autoloader, the Composer autoloader can still autoload extension classes for you.
+在你不使用 Yii 的自动加载器时，Composer 的自动加载器仍然可以帮你自动加载扩展内的类。
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