Fix ODR violations with nested static constexpr function objects

Fixes #75
Fixes #76

include/boost/hana/comparable.hpp

@@ -93,7 +93,7 @@ namespace boost { namespace hana {
 
     //! @cond
     template <typename X>
-    constexpr decltype(auto) _equal::_to::operator()(X&& x) const
+    constexpr decltype(auto) _equal_to::operator()(X&& x) const
     { return hana::partial(equal, static_cast<X&&>(x)); }
     //! @endcond
 
@@ -127,7 +127,7 @@ namespace boost { namespace hana {
 
     //! @cond
     template <typename X>
-    constexpr decltype(auto) _not_equal::_to::operator()(X&& x) const
+    constexpr decltype(auto) _not_equal_to::operator()(X&& x) const
     { return hana::partial(not_equal, static_cast<X&&>(x)); }
     //! @endcond
 

include/boost/hana/detail/insert_fwd.hpp

@@ -10,6 +10,7 @@ Distributed under the Boost Software License, Version 1.0.
 #ifndef BOOST_HANA_DETAIL_INSERT_FWD_HPP
 #define BOOST_HANA_DETAIL_INSERT_FWD_HPP
 
+#include <boost/hana/detail/static_constexpr.hpp>
 #include <boost/hana/fwd/core/datatype.hpp>
 #include <boost/hana/fwd/core/when.hpp>
 
@@ -31,7 +32,9 @@ namespace boost { namespace hana {
         }
     };
 
-    constexpr _insert insert{};
+    namespace {
+        constexpr auto const& insert = detail::static_constexpr<_insert>;
+    }
 }} // end namespace boost::hana
 
 #endif // !BOOST_HANA_DETAIL_INSERT_FWD_HPP

include/boost/hana/detail/keys_fwd.hpp

@@ -10,6 +10,7 @@ Distributed under the Boost Software License, Version 1.0.
 #ifndef BOOST_HANA_DETAIL_KEYS_FWD_HPP
 #define BOOST_HANA_DETAIL_KEYS_FWD_HPP
 
+#include <boost/hana/detail/static_constexpr.hpp>
 #include <boost/hana/fwd/core/datatype.hpp>
 #include <boost/hana/fwd/core/when.hpp>
 
@@ -30,7 +31,9 @@ namespace boost { namespace hana {
         }
     };
 
-    constexpr _keys keys{};
+    namespace {
+        constexpr auto const& keys = detail::static_constexpr<_keys>;
+    }
 }} // end namespace boost::hana
 
 #endif // !BOOST_HANA_DETAIL_KEYS_FWD_HPP

include/boost/hana/detail/static_constexpr.hpp

@@ -0,0 +1,34 @@
+/*!
+@file
+Defines `boost::hana::detail::static_constexpr`.
+
+@copyright Louis Dionne 2015
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+ */
+
+#ifndef BOOST_HANA_DETAIL_STATIC_CONSTEXPR_HPP
+#define BOOST_HANA_DETAIL_STATIC_CONSTEXPR_HPP
+
+namespace boost { namespace hana { namespace detail {
+    template <typename T>
+    struct _static_constexpr {
+        static constexpr T value{};
+    };
+
+    template <typename T>
+    constexpr T _static_constexpr<T>::value;
+
+    //! @ingroup group-details
+    //! Workaround to avoid ODR violations when declaring `static constexpr`
+    //! objects.
+    //!
+    //! See [this paper][1] for a detailed explanation of how to use this
+    //! utility.
+    //!
+    //! [1]: http://ericniebler.github.io/std/wg21/D4381.html
+    template <typename T>
+    constexpr auto const& static_constexpr = _static_constexpr<T>::value;
+}}} // end namespace boost::hana::detail
+
+#endif // !BOOST_HANA_DETAIL_STATIC_CONSTEXPR_HPP

include/boost/hana/ext/boost/fusion/detail/common.hpp

@@ -61,7 +61,7 @@ namespace boost { namespace hana {
     //////////////////////////////////////////////////////////////////////////
     template <typename S>
     struct models_impl<Sequence, S, when<detail::is_fusion_sequence<S>{}()>>
-        : decltype(true_)
+        : _integral_constant<bool, true>
     { };
 }} // end namespace boost::hana
 

include/boost/hana/ext/boost/tuple.hpp

@@ -117,7 +117,7 @@ namespace boost { namespace hana {
     //////////////////////////////////////////////////////////////////////////
     template <>
     struct models_impl<Sequence, ext::boost::Tuple>
-        : decltype(true_)
+        : _integral_constant<bool, true>
     { };
 }} // end namespace boost::hana
 

include/boost/hana/ext/std/tuple.hpp

@@ -191,7 +191,7 @@ namespace boost { namespace hana {
     //////////////////////////////////////////////////////////////////////////
     template <>
     struct models_impl<Sequence, ext::std::Tuple>
-        : decltype(true_)
+        : _integral_constant<bool, true>
     { };
 }} // end namespace boost::hana
 

include/boost/hana/foldable.hpp

@@ -319,6 +319,24 @@ namespace boost { namespace hana {
         }
     };
 
+    //////////////////////////////////////////////////////////////////////////
+    // reverse_fold
+    //////////////////////////////////////////////////////////////////////////
+    //! @cond
+    template <typename Xs, typename S, typename F>
+    constexpr decltype(auto) _reverse_fold::operator()(Xs&& xs, S&& s, F&& f) const {
+        return hana::fold.right(static_cast<Xs&&>(xs),
+                                static_cast<S&&>(s),
+                                hana::flip(static_cast<F&&>(f)));
+    }
+
+    template <typename Xs, typename F>
+    constexpr decltype(auto) _reverse_fold::operator()(Xs&& xs, F&& f) const {
+        return hana::fold.right(static_cast<Xs&&>(xs),
+                                hana::flip(static_cast<F&&>(f)));
+    }
+    //! @endcond
+
     //////////////////////////////////////////////////////////////////////////
     // for_each
     //////////////////////////////////////////////////////////////////////////
@@ -683,6 +701,15 @@ namespace boost { namespace hana {
         }
     };
 
+    //////////////////////////////////////////////////////////////////////////
+    // fuse
+    //////////////////////////////////////////////////////////////////////////
+    //! @cond
+    template <typename F>
+    constexpr decltype(auto) _fuse::operator()(F&& f) const
+    { return hana::partial(hana::flip(hana::unpack), static_cast<F&&>(f)); }
+    //! @endcond
+
     //////////////////////////////////////////////////////////////////////////
     // models
     //////////////////////////////////////////////////////////////////////////

include/boost/hana/functional/always.hpp

@@ -12,6 +12,7 @@ Distributed under the Boost Software License, Version 1.0.
 
 #include <boost/hana/config.hpp>
 #include <boost/hana/detail/create.hpp>
+#include <boost/hana/detail/static_constexpr.hpp>
 #include <boost/hana/detail/std/move.hpp>
 
 
@@ -58,7 +59,9 @@ namespace boost { namespace hana {
         { return detail::std::move(val_); }
     };
 
-    constexpr detail::create<_always> always{};
+    namespace {
+        constexpr auto const& always = detail::static_constexpr<detail::create<_always>>;
+    }
 #endif
 }} // end namespace boost::hana
 

include/boost/hana/functional/apply.hpp

@@ -10,6 +10,9 @@ Distributed under the Boost Software License, Version 1.0.
 #ifndef BOOST_HANA_FUNCTIONAL_APPLY_HPP
 #define BOOST_HANA_FUNCTIONAL_APPLY_HPP
 
+#include <boost/hana/detail/static_constexpr.hpp>
+
+
 namespace boost { namespace hana {
     //! @ingroup group-functional
     //! Invoke `f` with `x...` as arguments.
@@ -40,7 +43,9 @@ namespace boost { namespace hana {
         }
     };
 
-    constexpr _apply apply{};
+    namespace {
+        constexpr auto const& apply = detail::static_constexpr<_apply>;
+    }
 #endif
 }} // end namespace boost::hana
 

include/boost/hana/functional/arg.hpp

@@ -11,6 +11,7 @@ Distributed under the Boost Software License, Version 1.0.
 #define BOOST_HANA_FUNCTIONAL_ARG_HPP
 
 #include <boost/hana/config.hpp>
+#include <boost/hana/detail/static_constexpr.hpp>
 #include <boost/hana/detail/std/enable_if.hpp>
 #include <boost/hana/detail/std/size_t.hpp>
 
@@ -132,8 +133,10 @@ namespace boost { namespace hana {
         { return _arg<n - 25>{}(static_cast<Xn&&>(xn)...); }
     };
 
-    template <detail::std::size_t n>
-    constexpr _arg<n> arg{};
+    namespace {
+        template <detail::std::size_t n>
+        constexpr auto const& arg = detail::static_constexpr<_arg<n>>;
+    }
 #endif
 }} // end namespace boost::hana
 

include/boost/hana/functional/capture.hpp

@@ -12,6 +12,7 @@ Distributed under the Boost Software License, Version 1.0.
 
 #include <boost/hana/detail/closure.hpp>
 #include <boost/hana/detail/create.hpp>
+#include <boost/hana/detail/static_constexpr.hpp>
 #include <boost/hana/functional/partial.hpp>
 
 
@@ -74,7 +75,9 @@ namespace boost { namespace hana {
         }
     };
 
-    constexpr _make_capture capture{};
+    namespace {
+        constexpr auto const& capture = detail::static_constexpr<_make_capture>;
+    }
 #endif
 }} // end namespace boost::hana
 

include/boost/hana/functional/compose.hpp

@@ -12,6 +12,7 @@ Distributed under the Boost Software License, Version 1.0.
 
 #include <boost/hana/config.hpp>
 #include <boost/hana/detail/create.hpp>
+#include <boost/hana/detail/static_constexpr.hpp>
 #include <boost/hana/detail/std/move.hpp>
 #include <boost/hana/detail/variadic/foldl1.hpp>
 
@@ -102,7 +103,9 @@ namespace boost { namespace hana {
         }
     };
 
-    constexpr _make_compose compose{};
+    namespace {
+        constexpr auto const& compose = detail::static_constexpr<_make_compose>;
+    }
 #endif
 }} // end namespace boost::hana
 

include/boost/hana/functional/curry.hpp

@@ -107,8 +107,10 @@ namespace boost { namespace hana {
         operator()(F&& f) const { return {static_cast<F&&>(f)}; }
     };
 
-    template <detail::std::size_t n>
-    constexpr _make_curry<n> curry{};
+    namespace {
+        template <detail::std::size_t n>
+        constexpr auto const& curry = detail::static_constexpr<_make_curry<n>>;
+    }
 
     namespace curry_detail {
         template <detail::std::size_t n>
@@ -127,7 +129,7 @@ namespace boost { namespace hana {
             static_assert(sizeof...(x) <= n,
             "too many arguments provided to boost::hana::curry");
             return curry_detail::curry_or_call<n - sizeof...(x)>(
-                partial(f, static_cast<X&&>(x)...)
+                hana::partial(f, static_cast<X&&>(x)...)
             );
         }
 
@@ -137,7 +139,7 @@ namespace boost { namespace hana {
             static_assert(sizeof...(x) <= n,
             "too many arguments provided to boost::hana::curry");
             return curry_detail::curry_or_call<n - sizeof...(x)>(
-                partial(f, static_cast<X&&>(x)...)
+                hana::partial(f, static_cast<X&&>(x)...)
             );
         }
 #endif
@@ -147,7 +149,7 @@ namespace boost { namespace hana {
             static_assert(sizeof...(x) <= n,
             "too many arguments provided to boost::hana::curry");
             return curry_detail::curry_or_call<n - sizeof...(x)>(
-                partial(detail::std::move(f), static_cast<X&&>(x)...)
+                hana::partial(detail::std::move(f), static_cast<X&&>(x)...)
             );
         }
     };

include/boost/hana/functional/demux.hpp

@@ -13,6 +13,7 @@ Distributed under the Boost Software License, Version 1.0.
 #include <boost/hana/config.hpp>
 #include <boost/hana/detail/closure.hpp>
 #include <boost/hana/detail/create.hpp>
+#include <boost/hana/detail/static_constexpr.hpp>
 #include <boost/hana/detail/std/move.hpp>
 
 
@@ -210,7 +211,9 @@ namespace boost { namespace hana {
         }
     };
 
-    constexpr detail::create<_pre_demux> demux{};
+    namespace {
+        constexpr auto const& demux = detail::static_constexpr<detail::create<_pre_demux>>;
+    }
 #endif
 }} // end namespace boost::hana
 

include/boost/hana/functional/fix.hpp

@@ -12,6 +12,7 @@ Distributed under the Boost Software License, Version 1.0.
 
 #include <boost/hana/config.hpp>
 #include <boost/hana/detail/create.hpp>
+#include <boost/hana/detail/static_constexpr.hpp>
 #include <boost/hana/detail/std/move.hpp>
 
 
@@ -58,7 +59,9 @@ namespace boost { namespace hana {
     template <typename F>
     struct _fix;
 
-    constexpr detail::create<_fix> fix{};
+    namespace {
+        constexpr auto const& fix = detail::static_constexpr<detail::create<_fix>>;
+    }
 
     template <typename F>
     struct _fix {

include/boost/hana/functional/flip.hpp

@@ -12,6 +12,7 @@ Distributed under the Boost Software License, Version 1.0.
 
 #include <boost/hana/config.hpp>
 #include <boost/hana/detail/create.hpp>
+#include <boost/hana/detail/static_constexpr.hpp>
 #include <boost/hana/detail/std/move.hpp>
 
 
@@ -67,7 +68,9 @@ namespace boost { namespace hana {
         }
     };
 
-    constexpr detail::create<_flip> flip{};
+    namespace {
+        constexpr auto const& flip = detail::static_constexpr<detail::create<_flip>>;
+    }
 #endif
 }} // end namespace boost::hana
 

include/boost/hana/functional/id.hpp

@@ -10,6 +10,9 @@ Distributed under the Boost Software License, Version 1.0.
 #ifndef BOOST_HANA_FUNCTIONAL_ID_HPP
 #define BOOST_HANA_FUNCTIONAL_ID_HPP
 
+#include <boost/hana/detail/static_constexpr.hpp>
+
+
 namespace boost { namespace hana {
     //! @ingroup group-functional
     //! The identity function -- returns its argument unchanged.
@@ -28,7 +31,9 @@ namespace boost { namespace hana {
         }
     };
 
-    constexpr _id id{};
+    namespace {
+        constexpr auto const& id = detail::static_constexpr<_id>;
+    }
 #endif
 }} // end namespace boost::hana
 

include/boost/hana/functional/infix.hpp

@@ -11,6 +11,7 @@ Distributed under the Boost Software License, Version 1.0.
 #define BOOST_HANA_FUNCTIONAL_INFIX_HPP
 
 #include <boost/hana/config.hpp>
+#include <boost/hana/detail/static_constexpr.hpp>
 #include <boost/hana/detail/std/decay.hpp>
 #include <boost/hana/detail/std/move.hpp>
 #include <boost/hana/detail/std/remove_cv.hpp>
@@ -180,7 +181,10 @@ namespace boost { namespace hana {
         }
     } // end namespace infix_detail
 
-    constexpr infix_detail::make_infix<false, false> infix{};
+    namespace {
+        constexpr auto const& infix =
+            detail::static_constexpr<infix_detail::make_infix<false, false>>;
+    }
 #endif
 }} // end namespace boost::hana