how is a return values stored?

hiho@ll i was just asking myself, if it is possible, to get the return value of a function after the function calls "return" (or throws an exception) and before the value is returned example: class A{

    public function __construct(){}
    public function __destruct(){
      // here i want the return value like:
      $retval = idontknowwhichfunction();
      print $retval; // this print's "test"
    }

} function B(){ $classvar = new A(); return "test"; } i thought it would be a very impressive function for that purpose for what i would need it: think about testing a big php application calling hundreds of functions and debugging them takes very long but if i could track the arguments (debug_back_trace() function) AND the return values (that's what i'm asking for) i could run a complete test and after this i could change the input values automated and compare it with the output i got before another option for this, would be just debugging of such applications cause it can be boring to debug big applications and with such a possibility i can reproduce the problem very fast and at any point within my application the question is: Q1: how is the return value (return or throw) stored within php?

     or another question would be: is it possible to write an extension which can retrieve every variable set within my php session? (i know of the security problems this produces, but until know, i'm evaluating if it can work) and would be the return value within this variables?

any hint on this would be great! since it's possible to create a sandbox within php (runkit extension) i think it should be possible to get the return value (or exception object) before the calling function receives it, not? Q2: maybe i didn't find it, but is there a finished php function which i can use like debug_back_trace but for the return value? Q3: anybody has another idea for such a "testing" or debugging environment?

     the main advantage of such a system would be: i can start debugging from any point within my code and i could very easily create automated test's which can compare the result (what it is and what it should be) "automated"

thx@ll