Laravel5.6 剖析 Facade 的运行机制

进入Laravel主目录的config文件中找到app.php

找到aliases对应类的函数，比如：'Mail' => Illuminate\Support\Facades\Mail::class,

新增：Facade 的 fake 方法来模拟事件监听，从而不是真正的执行

Facade内部使用了__callStatic 魔术方法，当未找到指定的静态方法时便会触发此函数，静态重载。
resolveFacadeInstance根据返回的别名，在Facade父类中会去调用容器获取该类的实例(如果还没有实例化的话)。
相当于app('mailer')

找到IOC容器中的MailServiceProvider类可以看到这里是注册了mailer

protected function registerIlluminateMailer()
{
$this->app->singleton('mailer', function ($app) {
$config = $app->make('config')->get('mail');

        // Once we have create the mailer instance, we will set a container instance
        // on the mailer. This allows us to resolve mailer classes via containers
        // for maximum testability on said classes instead of passing Closures.
        $mailer = new Mailer(
            $app['view'], $app['swift.mailer'], $app['events']
        );

        if ($app->bound('queue')) {
            $mailer->setQueue($app['queue']);
        }

        // Next we will set all of the global addresses on this mailer, which allows
        // for easy unification of all "from" addresses as well as easy debugging
        // of sent messages since they get be sent into a single email address.
        foreach (['from', 'reply_to', 'to'] as $type) {
            $this->setGlobalAddress($mailer, $config, $type);
        }

        return $mailer;
    });
}
    之后便可以使用mailer中的方法