Re: [eigen] Map const correctness now fixed

[Jim Bosch <talljimbo@xxxxxxxxx>]

On 12/10/2010 10:58 AM, Benoit Jacob wrote:
> 2010/12/10 Jim Bosch<talljimbo@xxxxxxxxx>:
> > On 12/10/2010 07:25 AM, Benoit Jacob wrote:
> > > This was bug 54,
> > > http://eigen.tuxfamily.org/bz/show_bug.cgi?id=54
> >
> > Excellent!
> >
> > This applies to Block, Transpose, and other things with DirectAccessBit set
> > too, right?
>
> There only ever was a problem with Map, right? Then, if you pass a Map
> as argument to other expressions, like Block<Map<...>  >, then yes
> everything propagates.

Here's an example:

void modify_matrix(Eigen::MatrixXd const & m) {
    Eigen::Transpose<Eigen::MatrixXd> t = m.transpose();
    b(0, 0) = 1.0;
}

My hope was that the const overload of MatrixBase::transpose() (and 
block(), and part(), etc.) would return a "Transpose<const T>" rather 
than a "Transpose<T> const" in order to ensure the above doesn't 
compile, and allow one to inadvertently modify a matrix passed by const 
reference.

Maybe one should never actually have a non-temporary Transpose or Block, 
but I've found doing that fairly useful in making code readable, and 
I've been hoping it is at worst neutral for performance purposes.


Jim