Is starting route grouping with namespace() not allowed in Laravel 5.4?

Question

Using Laravel 5.4, indeed in the documentation about Route grouping, and an example as this was given about namespacing:

Route::namespace('Admin')->group(function () {
   // Controllers Within The "App\Http\Controllers\Admin" Namespace
});

This according to the doc is okay, but after installing Laravel 5.4.30 I discovered that doing the above throws the following error:

PHP Parse error:  syntax error, unexpected 'namespace' (T_NAMESPACE) in /Applications/MAMP/htdocs/my_app/routes/web.php on line

Even though I did a workaround by using other route methods before it such as the following:

Route::prefix('')->namespace('Admin')->group(function () {
   // Controllers Within The "App\Http\Controllers\Admin" Namespace
});

Yet, Is this a bug in Laravel or something that I did't suspect is the issue in my code?.

If there is a need to provide more explanations, then I am glad to do that.

Update: As @Adweb suggested, it can be done using group(['namespace' => 'Admin'])... but I am really still keen on what could be the issue based on the error I got.

Here is my PHP version:

PHP 5.6.30 (cli) (built: Mar 11 2017 09:56:27) 
Copyright (c) 1997-2016 The PHP Group
Zend Engine v2.6.0, Copyright (c) 1998-2016 Zend Technologies

Answer 1

actually this name Route::namespace() we are using for this

Ex: when you have controller in Admin folder (App\Http\Controllers\Admin;) you can use like this

Route::namespace('Admin')->group(function () {
    Route::get('/home', 'HomeController@index');
}); 

so if don't use namespace then you have to use like this

Route::get('/home', 'Admin\HomeController@index');

but make sure in your HomeController in top you have to change namespace like this

namespace App\Http\Controllers; to namespace App\Http\Controllers\Admin;

I have checked with Laravel 5.4.3 Server - XAMPP PHP - 7.0 :)