Laravel Singleton 구현

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Http\Request;

class File extends Model
{
    // Singleton
    private static $singleton;

    public static function getInstance() {
        if(!isset(File::$singleton)) File::$singleton = new File('');
        return File::$singleton;
    }

    function __construct() {

    }
}