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Only define operator<< when all contained types are streamable (refs #31)

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Peter Dimov
2021-12-09 18:34:02 +02:00
parent e4b4b3f02b
commit 3fc7540733
3 changed files with 50 additions and 1 deletions
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1
test/Jamfile
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@@ -125,3 +125,4 @@ compile variant_derived_construct.cpp ;
run variant_visit_by_index.cpp ;
run variant_ostream_insert.cpp ;
run is_output_streamable.cpp ;

38
test/is_output_streamable.cpp Normal file
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@@ -0,0 +1,38 @@
// Copyright 2021 Peter Dimov
// Distributed under the Boost Software License, Version 1.0.
// https://www.boost.org/LICENSE_1_0.txt
#include <boost/variant2/variant.hpp>
#include <boost/core/lightweight_test_trait.hpp>
#include <ostream>
#include <string>
struct X
{
};
struct Y
{
};
std::ostream& operator<<( std::ostream& os, Y const& /*y*/ )
{
os << "Y()";
return os;
}
int main()
{
BOOST_TEST_TRAIT_TRUE((boost::variant2::detail::is_output_streamable<std::ostream, int>));
BOOST_TEST_TRAIT_TRUE((boost::variant2::detail::is_output_streamable<std::ostream, float>));
BOOST_TEST_TRAIT_TRUE((boost::variant2::detail::is_output_streamable<std::ostream, std::string>));
BOOST_TEST_TRAIT_FALSE((boost::variant2::detail::is_output_streamable<std::ostream, void>));
BOOST_TEST_TRAIT_FALSE((boost::variant2::detail::is_output_streamable<std::ostream, X>));
BOOST_TEST_TRAIT_TRUE((boost::variant2::detail::is_output_streamable<std::ostream, Y>));
BOOST_TEST_TRAIT_TRUE((boost::variant2::detail::is_output_streamable<std::ostream, boost::variant2::variant<int, float, std::string>>));
BOOST_TEST_TRAIT_FALSE((boost::variant2::detail::is_output_streamable<std::ostream, boost::variant2::variant<int, float, X>>));
BOOST_TEST_TRAIT_TRUE((boost::variant2::detail::is_output_streamable<std::ostream, boost::variant2::variant<int, float, Y>>));
return boost::report_errors();
}