Re: [eigen] An insistent plea for an input operator

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On Tue, Jul 20, 2010 at 4:51 PM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:
> 2010/7/20 Hauke Heibel <hauke.heibel@xxxxxxxxxxxxxx>:
>> I am not a big fan of this mainly due to safety reasons and
>> consistency reasons.
>> Currently, you can even use an ifstream since it is an istream.
> Sure! How is this a problem?

Not really but somebody might think hey, it accepts input from
std::cin in the form of

1 2 3
4 5 6

why not from a text file... I admit, we can easily deal with that. I
was more like brainstorming. ;)

>> We
>> also need to deal with the way in which the data is given. Why should
>> it be given as 1 2 3 4 ... and not 1,2,3,4
> I think the whole point is that just because we support 1 2 3 4
> doesn't prevent us from supporting other formats too. We can accept
> multiple formats and for the general solution (in the future) I would
> like input to support any Eigen::IOFormat, just like output does. But
> even then, I don't see how it could be a problem that we support the
> very simple default format 1 2 3 4 ?

I just can't see right now how we can use Eigen::IOFormat while
keeping the suggested API. We need something like a class providing
several static operator>> functions taking different parameters or
such. I don't doubt that this is doable, I am just wondering whether
we might be quickly introduce API breaks.

>> For me, the inclusion of such an operator must at least be optional,
>> i.e. not automatically through Dense, Core or Eigen. If it were in the
>> Eigen namespace, how would I provide my own version?
> Aaah, good point !!
> Indeed if we accept Helmut's operator, you can't provide your own anymore.
> At least not unless we do something about it. We could certainly
> provide Helmut's operator as a simple default while letting you
> override it; there are various ways we could achieve that in c++. (Let
> it call a function from a template helper struct that you can
> specialize, etc, etc).

Maybe, once the Eigen::IOFormat is specified this is then easily doable.

I just want to emphasize that I am not all against incorporating
extended IO functionality, I am just against quick shots which might
back fire...

- Hauke

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