In laravel 5.0 the way to define constants and use them through out the project. Following are the steps to accomplish it:-

Step 1st :- Creating a separate file under /config folder named as constants.php ( it can be any name) for storing all constants.

<?php
return [
    'CONTROLLER_PATH' => "App\Http\Controllers\\"
];

Step 2nd :- Define the file name in composer.json under "autoload" with "files" param for automatically loading the file.

"autoload": {
                "files": [
                    "config/constants.php"
                ]     }

Step 3rd :- Running the following command in command line.

$ composer dumpautoload 

Step 4th :- Syntax for using the constants.

Config::get('constants.CONTROLLER_PATH')