Re: [eigen] aliasing system

[Andre Krause <post@xxxxxxxxxxxxxxxx>]

Schleimer, Ben wrote:
> > The point of my example with rows was that if we want to determine if 
> > rows/columns/blocks/minors overlap in memory, we're trying to do something 
> > that can't be done at compile-time (because the arguments that you pass to 
> > these functions is not necessary a compile-time constant). Hence that will 
> > have a cost, and if you want to handle all cases it'll be a big cost (you'll 
> > have to check for each entry in the matrix if overlapping occurs at that 
> > entry).
>
> Umm, good point. I guess aliasing has to be documented then.
>
> Cheers
> ben

BUT i still would insist to have that check in _DEBUG mode only at 
runtime ! if it is possible without too much coding. it is very 
important to be able to somehow know that my code does what i assume it 
to do. and newbies and those who usually skip the FAQ and DOCs will be 
faced with strange errors if they try what seems to be a naturally 
equation: m=m*m.

but i have another idea:

if its too much trouble checking overlapping memories while dealing with 
expression templates,

might there be an easy way to simply turn of expression templates for 
debugging?

so i might compile my program with expression templates off, test if 
everything works fine, measure my performance. then i will switch on 
some #ifdef or whatever and test again, enjoying the performance boost 
of expression templates and additionally verify everything still works 
as expected.

and if it is not easy to switch off expression templates via some ifdef, 
then i would suggest the following:

first make eigen2 complete and working and near final,

then make in an concentrated effort of - lets say some days of 
programming - an eigen2_without_expression_templates !! maybe in another 
subdirectory. if it has the exact same interface, one could just 
exchange headers and do the tests if everything works fine.