Question:
How to get user list by role programmatically in Drupal8?
Solution:
first import User
class
use Drupal\user\Entity\User;
Thise code will be return user list of a role (administrator)
$ids = \Drupal::entityQuery('user')
->condition('status', 1)
->condition('roles', 'administrator')
->execute();
$users = User::loadMultiple($ids);
foreach($users as $user){
$username = $user->get('name')->getString();
$mail = $user->get('mail')->getString();
$userlist[$mail] = $username;
}