Class T4

test/value_from.cpp:86–92

BOOST_CORE_STATIC_ASSERT( ! ::boost::json::has_value_from<T3>::value );

struct T4
{
    operator ::boost::json::value()
    {
        return nullptr;
    }
};

BOOST_CORE_STATIC_ASSERT( ! ::boost::json::has_value_from<T4>::value );