ublas: reserve [Re: questions on ublas ?]

From: jhrwalter (walter_at_[hidden])
Date: 2001-12-08 07:20:29

--- In boost_at_y..., Peter Schmitteckert (boost) <boost_at_s...> wrote:
> Salut,
> 
> On Friday 07 December 2001 09:29, Toon Knapen wrote:
> > jhrwalter wrote:
> > > Do we really need reserve()? IMO the allocation behaviour of 
resize()
> > > is a quality of implementation issue, especially since resize() 
is a
> > > method of the proxy concept. If we intend to make it's behaviour
> > > transparent, we'd have to introduce capacity() first.
> >
> > I find this really necessary (there's also a good reason why they 
have
> > capacity and size in std::vector). Everytime you shrink the 
vector or
> > matrix (i.e. resize(x) with x < size() ), you are going to delete
[] the
> > old data and new[] another array. This is very time consuming.
> > I would suggest to allign totally with what std::vector does : 
you can
> > resize without reallocation (if the capacity is large enough) and 
you
> > can easily shrink the capacity by copying to a smaller vector.
> 
> I agree.
> Allthough a submatrix adapter would be sufficient for me.

This is indeed an alternative. matrix_range should be an suited 
submatrix adaptor (with a poor name?). 
 
> > > BTW, do we need to consider std::allocator?
> >
> > In the long term : yes. But no allocater can be as smart as what 
you
> >
> > can do with capacity() and resize(). So the allocator is not a 
solution
> >
> > to the above problem.
> > An allocator would be nice e.g. to optimise allocation of many 
small
> > matrices.
> I agree.
> 
> Peter
 
Regards
 
Joerg