Re: [eigen] Qt's container support

[Alex Stapleton <alex.stapleton@xxxxxxxxxxxxx>]

2009/1/20 Gael Guennebaud <gael.guennebaud@xxxxxxxxx>:
> Hi all,
>
> I think that being able to store Eigen's matrices in Qt's containers
> is very important (especially QVector<>), and just like std::vector,
> there are a couple of issues:

> Issue 2:
> the second problem is to enforce QVector to allocate aligned memory
> buffers. Fortunately, Qt's developers had the good idea to define
> wrapper functions around malloc/free/realloc called qMalloc, qFree
> etc.
> So the workaround is simply to redefine these functions to call
> ei_align_malloc. I added a Eigen/QtAlignedMalloc header which exactly
> does that (I'll commit it once the next issue will be solved).
> => PROBLEM SOLVED

I am not a Qt person in general so please correct me if I am wrong but
wont this will result in *all* QVectors using aligned allocation?

> Issue3:
> The last issue I found is with QVector::fill(const T&,size_t) which is
> the equivalent of std::vector<T>::resize(size_t,T). Here the argument
> is passed by reference so no alignment issue. The problem is the use
> of the default ctor and operator= to initialize/copy the new elements
> while our operator= does not allow to set an uninitialized matrix.
> Solutions:
>  a) allow operator= to set/resize an uninitialized matrix
>  b) specialize QVector for Eigen's matrix type using a similar trick
> than for std::vector such that we only have to redefine the fill()
> method to use Matrix::set()
>  c) do nothing and enforce the user to use .resize() followed by a for
> loop instead of fill().
>
> I vote for solution b)
>
> any opinion ?

I vote for (b) too (and echo the "not a trick" sentiments from
Cyrille, but then I am biased :) Can probably farm some of the boiler
plate out into a macro aswell I think.