[boost] C++0x and Boost

From: Douglas Gregor (doug.gregor_at_[hidden])
Date: 2006-11-22 11:37:08

The C++ committee has been working on the upcoming revision of the ISO C
++ standard, C++0x, which will include several new features that are
likely to be of interest to Boost developers and users. As C++0x draws
nearer, we are starting to see preliminary implementations of C++0x
features. We need more experience with the use of these new language
features to better understand how well they work. Boost can help the C++
community gain valuable experience with these features by upgrading and
extending existing Boost libraries with these new language features.

To support this goal, I have committed a set of changes to the Boost
config library (on CVS HEAD), which add several new macros to indicate
the availability of C++0x features. The list involves only features that
I know have been implemented; see below for the compilers that support
various features. The new configuration macros are:

  BOOST_CXX0X_LONG_LONG: long long support (aliases BOOST_HAS_LONG_LONG)
  BOOST_CXX0X_PREPROCESSOR: C99 preprocessor extensions
  BOOST_CXX0X_RVALUE_REFERENCES: rvalue references
  BOOST_CXX0X_STATIC_ASSERT: static assertions
  BOOST_CXX0X_CONCEPTS: concepts (not yet accepted)
  BOOST_CXX0X_VARIADIC_TEMPLATES: variadic templates (not yet accepted) 

This list will grow as more C++0x features become available in
compilers. Still, we can now use these macros within Boost libraries
however we want. For example, I added the following to
boost/static_assert.hpp:

  #ifdef BOOST_CXX0X_STATIC_ASSERT
  #  define BOOST_STATIC_ASSERT( B ) static_assert(B, #B)
  #else
  // today's library-defined BOOST_STATIC_ASSERT
  #endif

The error messages when using a compiler supporting static_assert are
much more useful.

I know of support for the following C++0x features in publicly available
compilers:

Rvalue references:
  - Metrowerks CodeWarrior 10: no link; the compiler was discontinued :(

Static assertions:
  - GCC 4.3.0: http://gcc.gnu.org/gcc-4.3/changes.html (in active
development)

Concepts:
  - ConceptGCC: http://www.generic-programming.org/software/ConceptGCC/

Variadic templates:
  - Patch against GCC:
http://www.generic-programming.org/~dgregor/cpp/variadic-templates.html

I plan to start nightly Boost regression tests for some of these
compilers, so we can track our progress on C++0x support. 

We get to play with cool new language features *and* help the C++
community at large. What could be better than that?

  Cheers,
  Doug