A mostly unknown perhaps useless but sorta neat PHP coding trick

Yesterday while documenting that PHP 6 deprecates $string{42} in favor of $string[42] I stumbled upon a comment within the PHP Manual XML sources, and here it is in its entirety:

<!-- maybe it's better to leave this out?? 
// this works, but i disencourage its use, since this is NOT 
// involving functions, rather than mere variables, arrays and objects.
$beer = 'Heineken';
echo "I'd like to have another {${ strrev('reeb') }}, hips";
 -->

The thought of a function being called from within a string (without eval()) seems a little odd, doesn't it? Well, the above code in fact works. Not sure how useful it is but likely someone will find a creative use or two. The internals team generally feels that the behavior isn't worth documenting as it's simply an ugly and poor coding style BUT, maybe you'll see it (the "{${ func() }}" syntax) on a PHP exam somewhere so now you know... :-)

History: This information was added within a patch titled "Added jeroen's updates" by Damien Seguy apparently for Jeroen van Wolffelaar on the date Thu May 10 18:01:04 2001 UTC.

Update (April 20, 2007): A few days ago Jani demonstrated a simpler example for these variable functions:

$exec = 'shell_exec';
$cmd = 'ls -l';
echo "This is embedded exec: {$exec($cmd)}";