Thanks Jim, adding the extra parentheses solved the problem.
I'll contact the Boost.Variant people.
- bryan
On Tue, May 7, 2013 at 4:28 PM, Jim Bosch <tallji...@gmail.com> wrote:
> On 05/07/2013 07:19 PM, Bryan Catanzaro wrote:
>
>> Hi -
>> Using Boost 1.53.0, the following code fails to compile with g++, when
>> c++11 is enabled:
>>
>> #include <boost/python.hpp>
>> #include <boost/variant.hpp>
>>
>> struct A{}; struct B{};
>>
>> typedef boost::variant<A, B> my_variant;
>>
>> void foo(boost::python::object o) {
>> my_variant v = boost::python::extract<my_**variant>(o);
>> }
>>
>> The error is:
>> /home/bcatanzaro/boost_1_53_0/**boost/variant/variant.hpp:**1574:9:
>> error: no matching function for call to ‘boost::variant<A,
>> B>::initializer::initialize(**void*, std::remove_reference<boost::**
>> python::extract<boost::**variant<A, B> >&>::type)’
>>
>> Looking at the relevant line in boost/variant/variant.hpp, it looks like
>> variant is attempting to convert the boost::python::extract<my_**variant>
>> object into either A or B, and failing to find a conversion. Since this
>> code compiles when c++11 is not enabled, it appears rvalue references
>> coupled with boost::python::extract are confusing boost::variant's
>> constructor selection; I would expect it should be copy constructing from
>> variant<A, B>, rather than convert constructing into A or B.
>>
>> Any advice or workarounds? Turning off c++11 is difficult, since the
>> whole project relies on it. The code compiles correctly with c++11 turned
>> on with Boost 1.48.0, so it appears something has regressed.
>>
>>
> Hmm...maybe try this?
>
> my_variant v = boost::python::extract<my_**variant>(o)();
>
> (note the extra parenthesis). Or this:
>
> my_variant v = boost::python::extract<my_**variant const &>(o)();
>
> I haven't checked, but I'd be very surprised if the change between 1.48
> and 1.53 was in Boost.Python, so that means you can probably reproduce it
> without Boost.Python and maybe report it to the Boost.Variant people as a
> regression there.
>
>
> Jim
>
>
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