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117 lines
4.9 KiB
117 lines
4.9 KiB
From cbdb354a274c8ab51a15dd43eafd02c2b6a576f0 Mon Sep 17 00:00:00 2001
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From: Edward Catmur <edward.catmur@mavensecurities.com>
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Date: Wed, 17 Apr 2019 15:05:37 +0100
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Subject: [PATCH 1/2] Copy variant cvref when determining result type
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Ensures that we can e.g. call apply_visitor on a lvalue variant
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---
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boost/variant/detail/apply_visitor_unary.hpp | 9 +++++----
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1 file changed, 5 insertions(+), 4 deletions(-)
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--- a/boost/variant/detail/apply_visitor_unary.hpp
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+++ b/boost/variant/detail/apply_visitor_unary.hpp
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@@ -23,6 +23,7 @@
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# include <boost/mpl/size.hpp>
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# include <boost/utility/declval.hpp>
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# include <boost/core/enable_if.hpp>
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+# include <boost/type_traits/copy_cv_ref.hpp>
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# include <boost/type_traits/remove_reference.hpp>
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# include <boost/variant/detail/has_result_type.hpp>
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#endif
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@@ -85,7 +86,7 @@ namespace detail { namespace variant {
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// This class serves only metaprogramming purposes. none of its methods must be called at runtime!
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template <class Visitor, class Variant>
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struct result_multideduce1 {
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- typedef typename Variant::types types;
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+ typedef typename remove_reference<Variant>::type::types types;
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typedef typename boost::mpl::begin<types>::type begin_it;
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typedef typename boost::mpl::advance<
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begin_it, boost::mpl::int_<boost::mpl::size<types>::type::value - 1>
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@@ -95,14 +96,14 @@ struct result_multideduce1 {
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struct deduce_impl {
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typedef typename boost::mpl::next<It>::type next_t;
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typedef typename boost::mpl::deref<It>::type value_t;
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- typedef decltype(true ? boost::declval< Visitor& >()( boost::declval< value_t >() )
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+ typedef decltype(true ? boost::declval< Visitor& >()( boost::declval< copy_cv_ref_t< value_t, Variant > >() )
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: boost::declval< typename deduce_impl<next_t>::type >()) type;
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};
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template <class Dummy>
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struct deduce_impl<last_it, Dummy> {
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typedef typename boost::mpl::deref<last_it>::type value_t;
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- typedef decltype(boost::declval< Visitor& >()( boost::declval< value_t >() )) type;
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+ typedef decltype(boost::declval< Visitor& >()( boost::declval< copy_cv_ref_t< value_t, Variant > >() )) type;
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};
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typedef typename deduce_impl<begin_it>::type type;
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@@ -132,7 +133,7 @@ inline decltype(auto) apply_visitor(Visi
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boost::detail::variant::has_result_type<Visitor>
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>::type* = 0)
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{
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- boost::detail::variant::result_wrapper1<Visitor, typename remove_reference<Visitable>::type> cpp14_vis(::boost::forward<Visitor>(visitor));
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+ boost::detail::variant::result_wrapper1<Visitor, Visitable> cpp14_vis(::boost::forward<Visitor>(visitor));
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return ::boost::forward<Visitable>(visitable).apply_visitor(cpp14_vis);
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}
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--- a/libs/variant/test/const_ref_apply_visitor.cpp
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+++ b/libs/variant/test/const_ref_apply_visitor.cpp
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@@ -217,6 +217,44 @@ void test_cpp14_visitor(const variant_ty
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#endif
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}
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+void test_cpp14_visitor(variant_type& test_var)
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+{
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+ std::cout << "Testing lvalue visitable for c++14\n";
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+
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+ BOOST_TEST(boost::apply_visitor([](auto& v) { return lvalue_rvalue_detector()(v); }, test_var) == "lvalue reference");
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+}
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+
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+void test_cpp14_mutable_visitor(variant_type& test_var)
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+{
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+ std::cout << "Testing lvalue visitable for c++14 with inline mutable lambda\n";
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+
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+ BOOST_TEST(boost::apply_visitor([](auto& v) mutable -> auto { return lvalue_rvalue_detector()(v); }, test_var) == "lvalue reference");
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+}
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+
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+void test_cpp14_visitor(variant_type& test_var, variant_type& test_var2)
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+{
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+ std::cout << "Testing lvalue visitable for c++14\n";
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+
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+ BOOST_TEST(boost::apply_visitor([](auto& v, auto& vv) { return lvalue_rvalue_detector()(v, vv); }, test_var, test_var2)
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+ == "lvalue reference, lvalue reference");
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+}
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+
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+void test_cpp14_visitor(variant_type& test_var, variant_type& test_var2, variant_type& test_var3)
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+{
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+#if !defined(BOOST_VARIANT_DO_NOT_USE_VARIADIC_TEMPLATES) && !defined(BOOST_NO_CXX11_HDR_TUPLE)
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+ std::cout << "Testing lvalue visitable for c++14\n";
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+
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+ auto result = boost::apply_visitor([](auto& v, auto& t, auto& p) { return lvalue_rvalue_detector()(v, t, p); },
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+ test_var, test_var2, test_var3);
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+ std::cout << "result: " << result << std::endl;
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+ BOOST_TEST(result == "lvalue reference, lvalue reference, lvalue reference");
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+#else
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+ (void)test_var;
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+ (void)test_var2;
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+ (void)test_var3;
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+#endif
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+}
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+
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void test_cpp14_visitor(variant_type&& test_var)
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{
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std::cout << "Testing rvalue visitable for c++14\n";
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@@ -333,8 +371,14 @@ void run_cpp14_mixed_tests()
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void run_cpp14_tests()
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{
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#ifndef BOOST_NO_CXX14_DECLTYPE_AUTO
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+ variant_type const c1(10), c2(20), c3(30);
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variant_type v1(10), v2(20), v3(30);
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+ test_cpp14_visitor(c1);
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+ test_cpp14_mutable_visitor(c1);
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+ test_cpp14_visitor(c2, c3);
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+ test_cpp14_visitor(c1, c2, c3);
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+
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test_cpp14_visitor(v1);
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test_cpp14_mutable_visitor(v1);
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test_cpp14_visitor(v2, v3);
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