访问对象标识符，如var_dump？

var_dump function showing a object indentifier for each object output, for example:

$now = new \DateTimeImmutable();
var_dump($now);

The output is:

object(DateTimeImmutable)#412 (3) {
  ["date"]=>
  string(26) "2016-04-29 21:31:55.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(3) "UTC"
}

Is this 412 is unique in group of all current objects ?

How to access this number more efficently ?

I don't think that internal identifier is something you have to worry about. If you want to save variables and restoring them later, you can use serialize() and unserialize().

EDIT: may be spl_object_hash() could be what you need?

http://php.net/spl_object_hash