boost.variant broken in combination with g++ 4.6.x series and C++0x

[anonymous]

We observed compilation errors in case the main header of boost.signals2 has been included.

Example code :

#include <boost/signals2.hpp>

int main() { return 0; }

The following call fails with errors

g++-4.6.3 --std=c++0x main.cpp -I /opt/boost_1_54_0/

The error message points to some sections in boost.variant recently modified for boost 1.54.0 (I attached the rather lengthly error message).

In case c++0x is not activated or a 4.7/4.8-series version is used, the compilation succeeds.

We simply excluded the problematic section in file boost/variant/variant.hpp which resolved our compilation problem.

I saw that the gcc 4.6 series is not in the list of compilers tested with C++11 enabled but for us this section in variant is the first that fails in case the preprocessor macro BOOST_NO_CXX11_RVALUE_REFERENCES is not set.

[anonymous]

The error message generated by g++ 4.6.3

[anonymous]

Simple fix to disable specific variant optimizations relying on rvalue references.

[Antony Polukhin]

This can be fixed by removing typename B1, from first void assign_impl, making it look like:

        template <typename RhsT, typename B2>
        void assign_impl(
              RhsT& rhs_content
            , mpl::true_ // has_nothrow_copy
            , mpl::false_ // is_nothrow_move_constructible
            , B2 // has_fallback_type
            )

[anonymous]

Agreed, looks better. I didn't see the obvious ...

For me this bug can be closed after applying this patch to the trunk.

[Antony Polukhin]

(In [85080]) Fix compilation of Boost.Variants move assignment for situations when one of the variant template classes has nothrow copy constructor and throwing move constructor (refs #8772)

[Antony Polukhin]

(In [85087]) Fix test case (refs #8772)

[Antony Polukhin]

(In [85157]) Merge from trunk:

• make the library work on exception-disabled environments (fixes #8717)
• fix compilation of Boost.Variants move assignment for situations when one of the variant template classes has nothrow copy constructor and throwing move constructor (fixes #8772)
• mark move constructor of variant with BOOST_NOEXCEPT_IF (refs #7911)