[boost] Boost.Convert. Take 2.

Subject: [boost] Boost.Convert. Take 2.
From: Vladimir Batov (Vladimir.Batov_at_[hidden])
Date: 2014-02-09 22:58:48

Another day I came across a topic called "String to T conversions - 
getting it right this time 
<http://groups.google.com/a/isocpp.org/group/std-proposals/t/a9905ba8e4f33f3e>" 
on the "ISO C++ Standard - Future Proposals 
<https://groups.google.com/a/isocpp.org/forum/#%21forum/std-proposals>" 
that got me interested/curious. Unfortunately, it seemed more of a 
discussion rather than a proposed/deployable solution to the string 
conversion issue. Then, I searched Boost archives to see if there was 
any development in that string-to-type conversion domain since my 
unsuccessful proposal about three years ago:

From: Edward Diener <eldiener <at> tropicsoft.com>
Subject: [Review] Boost.Convert, review manager analysis 
<http://news.gmane.org/find-root.php?message_id=iq12fm%24k6c%241%40dough.gmane.org>
Newsgroups: gmane.comp.lib.boost.devel 
<http://news.gmane.org/gmane.comp.lib.boost.devel>, 
gmane.comp.lib.boost.user <http://news.gmane.org/gmane.comp.lib.boost.user>
Date: 2011-05-06 15:01:06 GMT (2 years, 39 weeks, 6 days, 23 hours and 
47 minutes ago)

Unfortunately I was not able to find anything. Apologies if I missed 
something major/serious (I was not exactly closely monitoring the list). 
Is anyone aware of any work done in the area? If not, then I am thinking 
if we could revisit the issue the original (and failed) Boost.Convert 
tried to address. I am not sure about others but for me that quite 
essential and seemingly simple task is still quite important. I was 
watching the development of the lexical_cast but did not see it going 
beyond its original frugal design. So, maybe we might have another look 
at the code that Boost.Convert has become and that I've been 
using/working on?.. Convert V2... From past experience calling it 
Boost.Convert seems quite premature. :-) I only put Boost.Convert in the 
title as a reminder for those who participated in the original review.

So, the code is at https://github.com/yet-another-user/boost.xtra. The 
docs are old (from the original proposal) so, if anyone interested, I'd 
suggest jumping right to the test/example code in libs/convert/test. 
Apologies for the inconvenience but for now I'll try to see if I should 
put any effort updating the docs for possible submission.

The main difference from the original proposal is that the complicated 
blob was split in to two separate components -- Convert API facade and a 
converter. Here it seems very similar to (same as?) boost::lexical_cast 
which provides a uniform API facade which in turn deploys additional 
functionality (op<<, op>>). Similarly, Convert V2 requires a converter 
to be specified for conversion:

     boost::cstringstream_based_converter ccnv; // char converter
     boost::wstringstream_based_converter wcnv; // wchar_t converter

Then,

     int a000 = convert<int>::from(not_int_str,   -1, ccnv);
     int a001 = convert<int>::from(std_str,       -1, ccnv);
     int a002 = convert<int>::from(c_str,         -1, ccnv);
     int a003 = convert<int>::from(wstd_str,      -1, wcnv);
     int a004 = convert<int>::from(wc_str,        -1, wcnv);

Now all the configuration (formatting, locales, etc.) is separate from 
the API facade and provided (or not) by the plugged in converter. The 
only available converter tringstream_based_converter allows something like:

         std::locale rus_locale (rus_locale_name);
         std::locale eng_locale ("");

         // Set locale, case, precision,
ccnv(std::setprecision(4))(std::scientific)(std::nouppercase);

         string double_rus = convert<string>::from(double_v01, 
ccnv(rus_locale)).value();
         string double_eng = convert<string>::from(double_v01, 
ccnv(eng_locale)).value();

Gosh, it's getting too long... cutting it short. The above is probably 
sufficient for those who participated in the original review. Those who 
did not might have a look at the (original and old) docs and the 
test/example code.

V.