where when laravel code example

Example 1: wherein laravel

DB::table('user')->whereIn('id', [100,200])->get();

Example 2: when in larevel

$role = $request->input('role');

$users = DB::table('users')
                ->when($role, function ($query, $role) {
                    return $query->where('role_id', $role);
                })
                ->get();