[boost] Re: [ANN] Format Lite

From: Jonathan Turkanis (technews_at_[hidden])
Date: 2004-11-09 12:24:49

"Martin" <adrianm_at_[hidden]> wrote in message
news:loom.20041109T081650-836_at_post.gmane.org...
> > the user could define. At some point, I decided it was bad manners to keep
> > changing a stream's locale.
>
> Why is it bad manners to set the streams locale? The default locale
> is "classic" but I always change it to the user's preferred locale. For some
> streams (e.g. to generate SQL statements) I specify classic locale to avoid
> locale based formatting.

Personally I don't feel strongly about it. But P.J.Plaugher, in his proposal to
add additional code convertion components to the standard library
(http://tinyurl.com/5hal5), mentions the fact that the components do not modify
a stream's locale as a feature. I thought others might share this view, and
didn't see any reason to prefer a locale-based solution, so I used pword
instead. Of course this can be reconsidered.

> A custom facet doesn't change the locale, it just adds new functionality to
> the existing locale just as pword adds new functionality to streams.

It does change the locale, but the new locale is mostly a copy of the old one.
(I'm sure you know this.)

> Both
> tribool and date_time library uses custom facets for the formatting.

Okay, then this change might improve consitency with the rest of Boost.

> > By the way, there would be one facet for each selector, e.g., sequence_punc<
> > vector<_>, char >.
>
> Yes, but that is not different from your manipulator implementation.

I'm aware of that.

> To make it easy you could have a facet where the constructor accepts a
> punctuate object. It would work something like this:
>
> std::locale mylocale(std::locale(), new sequence_punct(punctuate< pair<string,
> string> >("[ ", " : ", " ]"));
> stream.imbue(mylocale);
> stream << xxx

sequence_punct would need some template parameter, so it would be better to use
object generators, as in

   std::locale mylocale(std::locale(), punctuate_locale< pair<string, string>
>( ... ));

Or how about:

  std::locale mylocale = std::locale() + punctuate< pair<string, string> >(...);

:-)

?

> > I'm not yet familiar with the program options library. With lexical_cast,
> > there's no way to specify a locale, so I guess you're talking about setting
> the
> > global locale. Right? I'm afraid this might be bad manners, too.
>
> See above about bad manners but you are right about that the global locale
> needs to be changed. I suggested that program_options library should include
> an imbue method but I don't think the author agreed.
>
> lexical_cast is just broken.
>
> >Mybe I can provide both options.
>
> Should be easy, just check if the facet exists and if not check the pword.

Right, but get_punctuation() for tuple-like objects already checks for three
different facets using pword, and it really should be four (since I forgot to
allow users to specify a default punctuation sequence for all types.) Doubling
this would lead to a lot of checking.

Best Regards,
Jonathan