Getting size in memory of an object in PHP?

Would it not make sense to try serializing the object and reading the string length? Obviously it will be several bytes off because serialized string would have s:'string' therefore s:'' being extra bytes... unless serialize could be the same way that PHP stores objects???

so for example

$size = strlen(serialize($object));

Just a thought?

Another messy but possibly accurate thought:

Assuming a class instance variable that has been manipulated a few times since instantiation:

$DB; // database access class for eg.
$mem = memory_get_usage();
$DB_tmp = clone $DB;
$mem = memory_get_usage() - $mem;
unset($DB_tmp);

$mem could be the exact amount of memory allocated to $DB;