[aspectc-user] reset tjp->that()?

[Yan Mao]

Hello Mike,

just as Daniel said, AC++ use pass-by-value in advice body, then it is hard to change the object pointer. Maybe it's a inveterate problem? Although I would like to use AC++ to do something with those pointers.

Regards,

Yan 


-------- Original-Nachricht --------
Datum:  Sat, 9 Dec 2006 13:24:08 -0500
Von: "Michael Gong" <mwgong at cs.utoronto.ca>
An: "Yan Mao" <maoyan at gmx.net>, "Daniel Lohmann" <daniel.lohmann at informatik.uni-erlangen.de>
Betreff:  Re: Re: [aspectc-user] reset tjp->that()?

> Hi, Daniel & Yan,
> 
> It brings an interesting question.
> 
> The template works fine for this case.
> 
> > I am afraid what you are trying to achieve is not possible.
> > // Template, works for any class that offers a Release() method
> > template< class T > void Release( T*& _this ) {
> > _this->Release(); // destroy
> > _this = 0; // invalidate
> > }
> >
> 
> But how about I want to do the "invalidation" for method "Release2" , 
> "Release3", or etc ? Using template, you might have :
> 
> template< class T > void Release2( T*& _this ) {
>  _this->Release2(); // destroy
>  _this = 0; // invalidate
>  }
> 
> template< class T > void Release3( T*& _this ) {
>  _this->Release3(); // destroy
>  _this = 0; // invalidate
>  }
> 
> ...
> 
> 
> Looks familiar ? :-)
> 
> It is typical crosscutting concern, I think.
> 
> Since AOP is targeted to modularize crosscutting concern, can it be used 
> for this case ? More specifically, can AspectC++ capture it ?
> 
> Regards,
> 
> Mike
> 
> 
> 
> ----- Original Message ----- 
> From: "Yan Mao" <maoyan at gmx.net>
> To: "Daniel Lohmann" <daniel.lohmann at informatik.uni-erlangen.de>
> Cc: <aspectc-user at aspectc.org>
> Sent: Saturday, December 09, 2006 11:18 AM
> Subject: Re: Re: [aspectc-user] reset tjp->that()?
> 
> 
> Hello Daniel,
> 
> thank for the explation, it's very helpful.
> 
> regards,
> 
> Yan Mao
> 
> 
> 
> -------- Original-Nachricht --------
> Datum:  Fri, 08 Dec 2006 17:06:02 +0100
> Von: Daniel Lohmann <daniel.lohmann at informatik.uni-erlangen.de>
> An: aspectc-user at aspectc.org
> Betreff:  Re: [aspectc-user] reset tjp->that()?
> 
> > Hi Yan,
> >
> > I am afraid what you are trying to achieve is not possible.
> >
> > > //the C++ code
> > > ClassA *p = new ClassA();
> > > p->DoSomething();
> > > p->Release();
> > > //now i want to set p=NULL with AOP
> >
> > In C++ the object instance pointer (this) is always passed by-value.
> > Technically, it is passed as a "hidden" first parameter:
> >
> > class A {
> >    void Release();
> > };
> >
> > becomes (technically) something such as
> >
> > void ClassA::Release( ClassA* this ) {
> > // this is by-value parameter
> > }
> >
> > The object reference inside some method (this) is a copy of the 
> > original
> > parameter. The same holds for the value returned by tjp->that()   in
> > advice code, it is another value copy of the originally passed 
> > instance
> > pointer. It is not possible to affect the "original" from advice code.
> >
> > Side node:
> > The common C++ idiom to invalidate the reference when destroying an
> > instance is to use a non-member function:
> >
> > // Template, works for any class that offers a Release() method
> > template< class T > void Release( T*& _this ) {
> > _this->Release(); // destroy
> > _this = 0; // invalidate
> > }
> >
> > //the C++ code
> > ClassA *p = new ClassA();
> > p->DoSomething();
> > Release(p);
> > // now p == 0
> >
> >
> > Daniel
> 
> -- 
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