Is this code no longer viable in laravel 5?

So i'm just starting out as a junior dev, but what i know is pretty basic(i was honest with this and the company was ok with it). I was told to learn as much as i possibly could about php currently and to figure out some pimcore codes on my own.

Anyway, i'm currently taking a laravel tutorial from udemy and the instructor typed this line of code in routes, as there's no longer a single route file anymore in laravel 5, i went and put this in /route/web.php

Route::get('/admin/posts/a', array('as'=>'admin.home'), function(){
    $url=route('admin.home');
    return "this url is". $url;
});

It gave me a ReflectionException error on the page when i went to that url, is this code no longer viable in laravel 5? if so, how would i go about adapting it?

via Chebli Mohamed