[boost] Re: Proposal: BOOST_NO_TEMPLATED_STREAMS config macro and helpers

From: Gennaro Prota (gennaro_prota_at_[hidden])
Date: 2003-07-26 05:39:38

On Sat, 26 Jul 2003 01:08:00 -0400, "Eric Friedman"
<ebf_at_[hidden]> wrote:

>In adding output streaming support for variant, I've realized the
>standard library packaged with gcc 2.9.7 and below does not support the
>templated stream classes. I've also realized that Boost.Tuple features a
>workaround addressing this same problem, with a comment to add a defect
>macro to boost/config.hpp in the future.

The test in Boost.Tuple however is totally wrong (it just tests for
the compiler, while it should test for the library - also IIRC the
library that ships with gcc 2.95 doesn't have the templated iostreams
either).

I had this problem with dynamic_bitset and, after discussing it with
Phil Edwards (who is one of the maintainers of libstdc++), I came up
with the macro that is currently in

http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/boost-sandbox/boost-sandbox/boost/dynamic_bitset.hpp?rev=1.28&content-type=text/vnd.viewcvs-markup

Basically I just wanted to support pre-3.0 versions of libstdc++, at
least the ones that are still in wide usage, and I don't know whether
that macro actually detects all of them or not; but it worked on the
versions I tried it on and there appears to be nothing better to test
for (libstdc++ 3 identifies itself with a suitable macro, __GLIBCPP__,
but previous versions don't).

Of course I agree that having a single macro in a single place is
good, but your solution seems overkilling to me: consider that, though
there are cases where you are able, with a couple of macros, to write
an inserter or an extractor that works with both old and new
iostreams, there are many other cases where the two versions are quite
different; take a look, for instance, at the new dynamic_bitset
extractor: it is totally different from a (yet to come) old-iostreams
version because it uses the stream buffer directly and because it
takes into account throwing for eofbit, failbit, etc. In such cases I
don't claim that boost developers always write an old-iostream version
too, so your macros would probably be far less used than it might
appear at first sight)

Genny.