[aspectc-user] (no subject)

Olaf Spinczyk olaf at ivs.cs.uni-magdeburg.de
Thu May 30 16:09:41 CEST 2002


On Thursday, 30. May 2002 14:54, you wrote:
>  Yes, it helps, but it does not solve everything. I
> would like that the around advice finally returns a
> result.
>  A code like the following
>  SomeObject a=FctWhichWillBeArounded();
> will work correctly if the around advice returns void
> ?
>  So, if I understand you correctly, an around advice
> cannot have a return value? It seems to me incorrect,
> even if my advice contains several pointcuts with
> different return values. It's the user bussines to
> assure that the type declared in the advice will
> finally be returned. An example :
>  pointcut Fct1()= call("Type1 fct1()")
>  pointcut Fct2()= call("Type2 fct2()")
>  pointcut theTwo()=Fct1() || Fct2()
>  advice theTwo() : Type3* theTwo() {
>    proceed();
>    if resultType==Type1  return new Type3(1)
>    if resultType==Type2  return new Type3(2)
>  }
>  I hope that I am not completely wrong.
>  Thanks,
>     Florin Cremenescu

You are not complete wrong. I remember that we have changed the behavior of 
AspectC++ in that particular point at least once.

Remember that C++ is not Java. You have no garbage collector and you cannot 
simply return a generic "Object". If a caller of fct1() expects an integer as 
a result the around advice is not allowed to give out a float. If the caller 
of fct2() expect some other type then the advice must give out exactly that 
type. Therefore we can't simply give around advice one return type like you 
have suggested.
Nevertheless, AspectC++ offers an interface to access the return value and 
check the type at run-time. Here is an example (it is tested!) that shows how 
you can do this:

#include <stdio.h>

pointcut Fct1() = call("int fct1()");
pointcut Fct2() = call("float fct2()");

pointcut theTwo() = Fct1() || Fct2();

aspect Test
   advice theTwo() : around ()
      thisJoinPoint->action ().trigger ();
      printf ("result_type: %s\n", thisJoinPoint->resulttype ());
      void *result = thisJoinPoint->result ();
      switch (thisJoinPoint->resulttype ()[0])
	 case 'i': *(int*)result += 1; break;
	 case 'f': *(float*)result += 0.001; break;
	 default:  printf ("unexpected type\n");

int fct1 ()
   return 4711;

float fct2 ()
   return 0.815;

int main ()
   printf ("fct1: %d\nfct2: %f\n", fct1(), fct2());
   return 0;

Best regards,


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