Drupal 7 global variables vs. Drupal 8 services

Several Drupal 7 global values like global $language and global $user are also now accessed via services in Drupal 8 (and not global variables).

Drupal::languageManager()->getCurrentLanguage() and Drupal::currentUser()

Example:

$lang = \Drupal::languageManager()->getCurrentLanguage();
ksm($lang->getName());

$user = \Drupal::currentUser();
ksm($user->id());

Two ways to get the currentUser data:

1) Procedural code

$user = \Drupal::currentUser();
ksm($user->id());

or

2) OO code access the @current_user service, via dependency injection (DI)

$service = \Drupal::service('thirstysix.ex');
ksm($service->DisplayUserId());

For Example Code:

modules/custom/thirstysix/thirstysix.info.yml

name: Thirsty Six Custom Module
description: Custom Module
type: module
core: 8.x

modules/custom/thirstysix/thirstysix.services.yml

services:
  thirstysix.ex:
    class: Drupal\thirstysix\Customservice
    arguments: ['@current_user']

modules/custom/thirstysix/src/Customservice.php

<?php

  namespace Drupal\thirstysix;
  
  use Drupal\Core\Session\AccountProxy;

  /**
   * Drupal 8 service.
   */
  class Customservice {

    private $currentUser;

    /**
     * DependencyInjection.
     */
    public function __construct(AccountProxy $currentUser) {
      $this->currentUser = $currentUser;
    }

    /**
     * Returns a current Drupal user id.
     */
    public function DisplayUserId() {
      return $this->currentUser->id();
    }

  }