[Dune-devel] [Dune-Bugs][#683] Requesting value_type and unary operator-() in FieldVector.

[Christian Engwer]

As we decided a while ago not to implement them I didn't bother with
starting a new discussion, but feel free to open a dedicated bug
report. This "multiple-suggestions" issue should not be reopend, as
parts of it are implemented.

Christian

On Mon, Jun 29, 2015 at 03:56:07PM +0200, Jorrit Fahlke wrote:
> Am Mon, 29. Jun 2015, 10:07:01 +0200 schrieb Christian Engwer:
> > Date: Mon, 29 Jun 2015 10:07:01 +0200
> > From: Christian Engwer <christian.engwer at uni-muenster.de>
> > To: Oliver Sander <sander at igpm.rwth-aachen.de>
> > Cc: "dune-devel at dune-project.org" <dune-devel at dune-project.org>
> > Subject: Re: [Dune-devel] [Dune-Bugs][#683] Requesting value_type and unary
> >  operator-() in FieldVector.
> > > What's so bad about C++11?  We use that all over the place.  And did you measure the impact
> > > of those "expensive temporaries"?  I wouldn't be surprised if you had a hard time seeing their
> > > effect at all.  :-)
> > 
> > for 2.4 we decided on compiler compatibilities which prohibit the use
> > of std::move _in_ the core modules. If you want to measure the impact
> > feel free, but std::move was introduced exactly to avoid these
> > temporaries, as (in many cases) the compiler can't do this for you.
> 
> I have to agree with Oli here.
> 
> 1. std::move has nothing to do with it.  Not for FieldVector, which keeps all
>    its data within the class, so moves would be just as expensive as copies.
>    (And possibly even more expensive, because I've seen compilers that don't
>    do copy constructor elision any more if you explicitly specify std::move,
>    but that situation has hopefully improved since.)
> 
> 2. I doubt that after optimization there would be much left of a temporary in
>    the assembler code (for FieldVector; it depends on the class, of course).
> 
> Regards,
> Jö.
> 
> -- 
> Jorrit (Jö) Fahlke, Institute for Computational und Applied Mathematics,
> University of Münster, Orleans-Ring 10, D-48149 Münster
> Tel: +49 251 83 35146 Fax: +49 251 83 32729
> 
> featured product: Debian GNU/Linux - http://www.debian.org



-- 
Prof. Dr. Christian Engwer 
Institut für Numerische und Angewandte Mathematik
Fachbereich Mathematik und Informatik der Universität Münster
Einsteinstrasse 62
48149 Münster

E-Mail	christian.engwer at uni-muenster.de
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