#vendor/laravel/framework/src/Illuminate/Database/Eloquent/Builder.php:480
public function paginate($perPage = null, $columns = ['*'], $pageName = 'page', $page = null)
{
    $query = $this->toBase();
    $total = $query->getCountForPagination();
    $this->forPage(
      $page = $page ?: Paginator::resolveCurrentPage($pageName),
      $perPage = $perPage ?: $this->model->getPerPage()
    );
    return new LengthAwarePaginator($this->get($columns), $total, $perPage, $page, [
      'path' => Paginator::resolveCurrentPath(),
      'pageName' => $pageName,
    ]);
}

public function __construct($items, $total, $perPage, $currentPage = null, array $options = [])
{
    foreach ($options as $key => $value) {
      $this->{$key} = $value;
    }
    $this->total = $total;
    $this->perPage = $perPage;
    $this->lastPage = (int) ceil($total / $perPage);
    $this->path = $this->path != '/' ? rtrim($this->path, '/') : $this->path;
    $this->currentPage = $this->setCurrentPage($currentPage, $this->lastPage);
    $this->items = $items instanceof Collection ? $items : Collection::make($items);
}

[
  ['username'=>'zhangsan', 'age'=>26],
  ['username'=>'lisi', 'age'=>23],
  ['username'=>'wangwu', 'age'=>62],
  ['username'=>'zhaoliu', 'age'=>46],
  ['username'=>'wangmazi', 'age'=>25],
  ['username'=>'lanzi', 'age'=>24],
  ['username'=>'pangzi', 'age'=>21],
]

use Illuminate\Pagination\LengthAwarePaginator;
use Illuminate\Pagination\Paginator;
use Illuminate\Http\Request;
# 仅做演示 #
function userList(Request $request) {
  $users = [
    ['username'=>'zhangsan', 'age'=>26],
    ['username'=>'lisi', 'age'=>23],
    ['username'=>'wangwu', 'age'=>62],
    ['username'=>'zhaoliu', 'age'=>46],
    ['username'=>'wangmazi', 'age'=>25],
    ['username'=>'lanzi', 'age'=>24],
    ['username'=>'pangzi', 'age'=>21]
  ];
  $perPage = 3;
  if ($request->has('page')) {
      $current_page = $request->input('page');
      $current_page = $current_page <= 0 ? 1 :$current_page;
  } else {
      $current_page = 1;
  }
  $item = array_slice($users, ($current_page-1)*$perPage, $perPage); //注释1
  $total = count($users);
  $paginator =new LengthAwarePaginator($item, $total, $perPage, $currentPage, [
      'path' => Paginator::resolveCurrentPath(), //注释2
      'pageName' => 'page',
  ]);
  $userlist = $paginator->toArray()['data'];
  return view('userlist', compact('userlist', 'paginator'));
}

{{ $paginator->render() }}