Subject: [Boost-bugs] [Boost C++ Libraries] #12423: fusion::make_map breaks when passing references
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2016-08-30 15:51:30
#12423: fusion::make_map breaks when passing references
------------------------------+---------------------
Reporter: oleg00@⦠| Owner: djowel
Type: Bugs | Status: new
Milestone: To Be Determined | Component: fusion
Version: Boost 1.61.0 | Severity: Problem
Keywords: fusion make_map |
------------------------------+---------------------
When using variadic maps the following code doesn't compile:
{{{
int i = 0;
fusion::make_map<int>(ref(i));
}}}
Clang gives this error:
error : no matching constructor for initialization of 'detail::map_impl<0,
pair<int, int &> >'
1> : base_type(first, rest...)
1> ^ ~~~~~
There is a constructor in fusion::pair that can do the required
conversion:
{{{
template <typename Second2>
BOOST_FUSION_GPU_ENABLED
pair(Second2&& val
, typename boost::disable_if<is_lvalue_reference<Second2>
>::type* /* dummy */ = 0
, typename boost::enable_if<is_convertible<Second2, Second>
>::type* /*dummy*/ = 0
) : second(BOOST_FUSION_FWD_ELEM(Second, val)) {}
}}}
But it's not being invoked since there's no make_map function that takes
rvalue refs. I was able to make this work by adding another make_map
overload:
{{{
template <typename ...Key, typename ...T>
BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
inline map<
fusion::pair<
Key
, typename detail::as_fusion_element<T>::type
>...>
make_map(T &&... arg)
{
typedef map<
fusion::pair<
Key
, typename detail::as_fusion_element<T>::type
>...>
result_type;
return result_type(std::forward<T>(arg)...);
}
}}}
-- Ticket URL: <https://svn.boost.org/trac/boost/ticket/12423> Boost C++ Libraries <http://www.boost.org/> Boost provides free peer-reviewed portable C++ source libraries.
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