Refactor Str::pool method.

system/str.php

@@ -88,18 +88,14 @@ class Str {
      */
     private static function pool($type = 'alnum')
     {
-        if ($type == 'alnum')
+        switch ($type)
         {
+            case 'alnum':
                 return '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
-        }
+            
-        elseif ($type == 'alpha')
+            default:
-        {
                 return 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
         }
-        else
-        {
-            throw new \Exception("Unrecognized random pool [$type].");
-        }
     }
 
 }