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

[Daniel Lohmann]

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


Yan Mao schrieb:
> Hello there,
> I'd like to ask, if it is possible to reset the pointer tjp->that() of NULL?
> 
> say i have an object pointer, after i use it, i release it, and i wnat to set it as NULL with AOP.
> 
> //the C++ code
> ClassA *p = new ClassA();
> p->DoSomething();
> p->Release();
> //now i want to set p=NULL with AOP
> 
> //the AOP Code:
> advice call("% ...::Release()"):after(){
>   tjp->that()=NULL;
> }
> 
> but i got the error C2106, "=": Linker Operand muss ein L-Wert Sein.
> 
> regards,
> 
> Yan Mao
> 
>