PHP中的闭包回调（Laravel 5）

Question

I am learning Laravel 5, and getting a little bit confused at these lines of code (creation of service provider):

 public function register()
{
    $this->app->singleton('Riak\Contracts\Connection', function($app)
    {
        return new Connection($app['config']['riak']);
    });
}

I cant understand $app variable, and frome where it will be passed into function? Thanks!

PS And please correct if I wrong, I read some posts, and how I understand closures is a anonimous functions what uses vars from outside scope (by using use () ), and lambda functions is just closure what doesnt use these vars. Or I miss something?

Answer 1

是$this->app->singleton ，它在调用时将$app传递给回调闭包。

Answer 2

The anonymous function is a Callable which is passed to the function singleton in the object $app .

The function singleton then calls the Callable (anonymous function) that you passed to it, and passes $app as argument into the anonymous function.