Yii2 Yii:: $app $app where is this variable instantiated?

The most commonly used service locator is the application (application) object, which can be accessed by \yii:: $app

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The most commonly used service locator is the application (application) object, which can be accessed by \yii:: $app

Look at the source code to know, if your application is a Web application, its index.php
(new yii\web\Application($config))->run();
The constructor of the application is called, and its inherited self- yii\base\Application constructed method is

public function __construct($config = []){    Yii::$app = $this;    $this->setInstance($this);    $this->state = self::STATE_BEGIN;    $this->preInit($config);    $this->registerErrorHandler($config);    Component::__construct($config);}

After the specific instantiation process, you can continue to view the source code in a sequential order. What questions can you leave a message, view the source code can help you quickly understand the initialization of yiiframework and the operation process

It's a magical variable!

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