PHP: Cast variable to null

Update: Since posting this 9 years ago, casting to unset has changed behavior and is deprecated. The last defined behavior was equivalent to setting the variable equal to NULL. You can either set the variable equal to NULL to retain the variable but indicate it has no value, or you can call the unset function to remove it entirely.

Original Answer:

$a = (unset) $a;

See type casting.

use (unset) instead of (null).

According to the Type casting section of the Type Juggling manual page, you can achieve this via...

$varName = (unset)$varName;