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Merged
apolukhin merged 1 commit into from
Jan 23, 2018
Merged

Perfect forwarding for passing visitor in apply_visitor. #40

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21 changes: 5 additions & 16 deletions include/boost/variant/detail/apply_visitor_unary.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -155,9 +155,9 @@ struct result_wrapper1
{
typedef decltype(result_multideduce1<Visitor, Variant>::deduce()) result_type;

Visitor& visitor_;
explicit result_wrapper1(Visitor& visitor) BOOST_NOEXCEPT
: visitor_(visitor)
Visitor&& visitor_;
explicit result_wrapper1(Visitor&& visitor) BOOST_NOEXCEPT
: visitor_(::boost::forward<Visitor>(visitor))
{}

template <class T>
Expand All @@ -169,26 +169,15 @@ struct result_wrapper1
}} // namespace detail::variant

template <typename Visitor, typename Visitable>
inline decltype(auto) apply_visitor(Visitor& visitor, Visitable&& visitable,
inline decltype(auto) apply_visitor(Visitor&& visitor, Visitable&& visitable,
typename boost::disable_if<
boost::detail::variant::has_result_type<Visitor>
>::type* = 0)
{
boost::detail::variant::result_wrapper1<Visitor, typename remove_reference<Visitable>::type> cpp14_vis(visitor);
boost::detail::variant::result_wrapper1<Visitor, typename remove_reference<Visitable>::type> cpp14_vis(::boost::forward<Visitor>(visitor));
return ::boost::forward<Visitable>(visitable).apply_visitor(cpp14_vis);
}

template <typename Visitor, typename Visitable>
inline decltype(auto) apply_visitor(const Visitor& visitor, Visitable&& visitable,
typename boost::disable_if<
boost::detail::variant::has_result_type<Visitor>
>::type* = 0)
{
boost::detail::variant::result_wrapper1<const Visitor, typename remove_reference<Visitable>::type> cpp14_vis(visitor);
return ::boost::forward<Visitable>(visitable).apply_visitor(cpp14_vis);
}


#endif // !defined(BOOST_NO_CXX14_DECLTYPE_AUTO) && !defined(BOOST_NO_CXX11_DECLTYPE_N3276)

} // namespace boost
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8 changes: 8 additions & 0 deletions test/const_ref_apply_visitor.cpp
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Expand Up @@ -190,6 +190,13 @@ void test_cpp14_visitor(const variant_type& test_var)
BOOST_CHECK(boost::apply_visitor([](auto&& v) { return lvalue_rvalue_detector()(FORWARD(v)); }, test_var) == "lvalue reference");
}

void test_cpp14_mutable_visitor(const variant_type& test_var)
{
std::cout << "Testing const lvalue visitable for c++14 with inline mutable lambda\n";

BOOST_CHECK(boost::apply_visitor([](auto&& v) mutable -> auto { return lvalue_rvalue_detector()(FORWARD(v)); }, test_var) == "lvalue reference");
}

void test_cpp14_visitor(const variant_type& test_var, const variant_type& test_var2)
{
std::cout << "Testing const lvalue visitable for c++14\n";
Expand Down Expand Up @@ -329,6 +336,7 @@ void run_cpp14_tests()
variant_type v1(10), v2(20), v3(30);

test_cpp14_visitor(v1);
test_cpp14_mutable_visitor(v1);
test_cpp14_visitor(v2, v3);
test_cpp14_visitor(v1, v2, v3);

Expand Down