Re: [eigen] aliasing system

[Andre Krause <post@xxxxxxxxxxxxxxxx>]

Benoît Jacob wrote:
> On Thursday 06 September 2007 16:02:15 Andre Krause wrote:
> > so then if there is no way to avoid this problem - what about a sort of
> > #pragma warning or assertion that gets thrown / printed in DEBUG mode
> > only, if a user tries to do
> >
> > m = m*m;
> >
> > is there some template magic available to detect this?
>
> Very good idea. Yes, I think that can be done with partial template 
> specialization. Will try.

wouldnt it be easier to compare the memory adresses of the objects?

suppose we have 2x2 matrices
u, v, w, and we do:
    u = v * w;

it will hopefully unroll to some function call to


typedef Matrix<float, 2,2> M;

void _ET_magic_generated_func(M& u, const M& v, const M& w)
{
	#ifdef _DEBUG
	if(&u == &v || &u == &w)
		std::cerr << "some warning!!";
	#endif

	u11 = v11*w11 + v12*w21;
	u21 = v21*w11 + v22*w21;
	u12 = v11*w12 + v12*w22;
	u22 = v21*w12 + v22*w22;
}


now, if we do the bad thing of

m = m*m;

it will detect that the pointers are identical and thus matrix product 
will get wrong result.