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Implemented ability to set fallback for tag_of (#263)

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This commit is contained in:
Denis Mikhailov
2022-12-22 06:16:10 +06:00
committed by GitHub
parent 0a2da9d0ac
commit d6298309fb
3 changed files with 58 additions and 1 deletions
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8
include/boost/fusion/support/tag_of.hpp Normal file → Executable file
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@@ -48,11 +48,17 @@ namespace boost { namespace fusion
{
BOOST_MPL_HAS_XXX_TRAIT_DEF(fusion_tag)
template<typename Sequence, typename Active=void>
struct tag_of_fallback
{
typedef non_fusion_tag type;
};
template <typename Sequence, typename Active>
struct tag_of_impl
: mpl::if_<fusion::detail::is_mpl_sequence<Sequence>,
mpl::identity<mpl_sequence_tag>,
mpl::identity<non_fusion_tag> >::type
mpl::identity<typename tag_of_fallback<Sequence>::type> >::type
{};
template <typename Sequence>

1
test/Jamfile Normal file → Executable file
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@@ -271,6 +271,7 @@ project
: [ requires cxx11_variadic_templates ] ]
[ compile support/tag_of.cpp ]
[ compile support/unused.cpp ]
[ compile support/detail/tag_of_fallback.cpp ]
# [ compile-fail xxx.cpp ]

50
test/support/detail/tag_of_fallback.cpp Executable file
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@@ -0,0 +1,50 @@
/*=============================================================================
Copyright (c) 2022 Denis Mikhailov
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
==============================================================================*/
#include <boost/fusion/support/tag_of.hpp>
#include <boost/static_assert.hpp>
#include <boost/type_traits/is_same.hpp>
#include <boost/core/enable_if.hpp>
#include <boost/mpl/bool.hpp>
#include <boost/mpl/if.hpp>
namespace mpl = boost::mpl;
template<typename T>
struct my_is_implicitly_reflectable;
namespace boost { namespace fusion
{
struct boost_my_reflectable_tag;
namespace detail
{
template<typename Sequence>
struct tag_of_fallback<Sequence, typename boost::enable_if<boost::is_same<Sequence, Sequence> >::type>
{
typedef typename mpl::if_<my_is_implicitly_reflectable<Sequence>
, boost_my_reflectable_tag
, non_fusion_tag
>::type type;
};
}
}}
struct reflectable {};
struct non_reflectable {};
template<typename T>
struct my_is_implicitly_reflectable : mpl::false_ {};
template<>
struct my_is_implicitly_reflectable<reflectable> : mpl::true_ {};
typedef boost::fusion::traits::tag_of<reflectable>::type ReflectableTag;
typedef boost::fusion::traits::tag_of<non_reflectable>::type NonReflectableTag;
BOOST_STATIC_ASSERT((boost::is_same<ReflectableTag, boost::fusion::boost_my_reflectable_tag>::value));
BOOST_STATIC_ASSERT((boost::is_same<NonReflectableTag, boost::fusion::non_fusion_tag>::value));
int
main() { }