Bug #1039 tmpdir and datadir not available via @@ system variable syntax

Description:
My specific need is for

  create TEMPORARY table ... DATA DIRECTORY=@@datadir

to work so I can create temporary table that are not stored in tmpdir
(which may be a swap space filesystem and too small to use in some cases).

Apart from making @@datadir available it may require changes to the parser.

How to repeat:
mysql> select @@datadir;
ERROR 1193: Unknown system variable 'datadir'

Suggested fix:
Make all system variables available via the @@ syntax for consistency.

This has been turned into a feature request

Is anyone considering to implement this? 

I sure hope so.

Actually, what I mean is the implementation of 

select @@datadir;

Not the ability to reference that value in a CREATE TABLE statement. 

It seems mighty odd that:

mysql> show variables like 'datadir';
+---------------+---------------------------------+
| Variable_name | Value                           |
+---------------+---------------------------------+
| datadir       | D:\MySQL\MySQL Server 5.1\Data\ |
+---------------+---------------------------------+
1 row in set (0.00 sec)

, but:

mysql> select @@datadir;
ERROR 1193 (HY000): Unknown system variable 'datadir'
mysql>

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/6131

Fixed in 5.0.22. Merge to 5.1 is still pending.

Fixed in 5.0.22 and 5.1.11.

Noted in 5.0.22, 5.1.11 changelogs.

The <literal>basedir</literal> and <literal>tmpdir</literal>
system variables could not be access via
<literal>@@<replaceable>var_name</replaceable></literal>
syntax. (Bug #1039)