为什么auth()->user()可以这样写，auth可以引出user()?

namespace App\Http\Controllers;

use App\Post;
use Illuminate\Http\Request;

class PostsController extends Controller
{
public function create(){
return view('posts.create');
}

public function store(){
$data=request()->validate([
'caption'=>'required',
'image'=>['required','image'],
]);
$imagePath=\request('image')->store('uploads','public');
auth()->user()->posts()->create([
'caption' => $data['caption'],
'image' => $imagePath,
]);


        return redirect('/profile/' . auth()->user()->id);
}
public function test(){

        var_dump(auth()->user());
}
}