Facades 類別名設定流程 (class_alias)

場景描述：

// web.php中
Route::get('/', function () {
    return view('welcome');
});

• 為何能直接使用Route,其實是呼叫了Illuminate\Support\Facades\Route類。然後通過facade獲取物件執行物件方法（看我上一篇文章facade原理）
• 為何呼叫Route也就呼叫了Illuminate\Support\Facades\Route類，這就是這篇文章的核心：
• class_alias：為一個類建立別名

核心程式碼 類：Illuminate\Foundation\AliasLoader

public function load($alias)
    {
        if (static::$facadeNamespace && strpos($alias, static::$facadeNamespace) === 0) {
            $this->loadFacade($alias);

            return true;
        }

      // $alias來自於config/app.php中aliases陣列中的一個鍵值隊如：       
      // 'Route' => Illuminate\Support\Facades\Route::class 中的鍵“Route”
        if (isset($this->aliases[$alias])) {
            //'Route' => Illuminate\Support\Facades\Route::class,
            // class_alias:為一個類建立別名
            return class_alias($this->aliases[$alias], $alias);
        }
    }

具體流程如下：

• 入口檔案index.php

  // 此處才包含了設定facade類別名的操作
  $response = $kernel->handle(
  $request = Illuminate\Http\Request::capture()
  );

• 進入Illuminate\Foundation\Http\Kernel類(Kernel.php)

  /**
   * Handle an incoming HTTP request.
   *
   * @param  \Illuminate\Http\Request  $request
   * @return \Illuminate\Http\Response
   */
  public function handle($request)
  {
      try {
          $request->enableHttpMethodParameterOverride();
          // 進入這行
          $response = $this->sendRequestThroughRouter($request);
      } catch (Exception $e) {
          $this->reportException($e);
  
          $response = $this->renderException($request, $e);
      } catch (Throwable $e) {
          $this->reportException($e = new FatalThrowableError($e));
  
          $response = $this->renderException($request, $e);
      }
  
      $this->app['events']->dispatch(
          new Events\RequestHandled($request, $response)
      );
  
      return $response;
  }

• 進入方法sendRequestThroughRouter

  protected function sendRequestThroughRouter($request)
  {
      // 將request物件繫結到容器$app的instances陣列裡面，實現單例模式
      $this->app->instance('request', $request);
  
      // 實際執行了這行 unset(static::$resolvedInstance["request"]);
      Facade::clearResolvedInstance('request');
  
      // 重點：這裡的操作包含執行了Facade類的別名設定
      $this->bootstrap();
  
      return (new Pipeline($this->app))
                  ->send($request)
                  ->through($this->app->shouldSkipMiddleware() ? [] : $this->middleware)
                  ->then($this->dispatchToRouter());
  }

• 進入bootstrap方法

  public function bootstrap()
  {
      if (! $this->app->hasBeenBootstrapped()) {
          // 執行容器例項$app裡面的bootstrapWith，攜帶引數是$this->bootstrappers()
          // $this->bootstrappers()最終返回的陣列是Kernel例項的屬性$bootstrappers
          // protected $bootstrappers = [
          //      \Illuminate\Foundation\Bootstrap\LoadEnvironmentVariables::class,
          //      \Illuminate\Foundation\Bootstrap\LoadConfiguration::class,
          //      \Illuminate\Foundation\Bootstrap\HandleExceptions::class,
          //      \Illuminate\Foundation\Bootstrap\RegisterFacades::class,
          //      \Illuminate\Foundation\Bootstrap\RegisterProviders::class,
          //      \Illuminate\Foundation\Bootstrap\BootProviders::class,
          // ];
          $this->app->bootstrapWith($this->bootstrappers());
      }
  }

• 進入Illuminate\Foundation\Application類的bootstrapWith方法

  public function bootstrapWith(array $bootstrappers)
  {
  
      $this->hasBeenBootstrapped = true;
  
      foreach ($bootstrappers as $bootstrapper) {
          $this['events']->dispatch('bootstrapping: '.$bootstrapper, [$this]);
          // 當迴圈到\Illuminate\Foundation\Bootstrap\RegisterFacades::class
          // Illuminate\Foundation\Bootstrap\RegisterFacades解析出類的RegisterFacades的例項物件
          // 呼叫RegisterFacades的bootstrap方法
          $this->make($bootstrapper)->bootstrap($this);
  
          $this['events']->dispatch('bootstrapped: '.$bootstrapper, [$this]);
      }
  }

• 進入Illuminate\Foundation\Bootstrap\RegisterFacades類，進入bootstrap方法

  /**
   * Bootstrap the given application.
   *
   * @param  \Illuminate\Contracts\Foundation\Application  $app
   * @return void
   */
  public function bootstrap(Application $app)
  {
      Facade::clearResolvedInstances();
  
      Facade::setFacadeApplication($app);
      // 這裡就是上面所說的 核心程式碼
      // 將config/app.php 裡的aliases陣列裡面的Facades類設定別名
      AliasLoader::getInstance(array_merge(
          $app->make('config')->get('app.aliases', []),
          $app->make(PackageManifest::class)->aliases()
      ))->register();
  }

• 進入Illuminate\Foundation\AliasLoader類，執行文章開頭說得核心程式碼