C++98 GCC 8 assignment does nothing

[Kojoley]

GCC 8.1.0/8.2.0/9.0.0 g++ -std=c++98 fails, g++ -std=c++11 is fine. The problem is not presented on GCC 7.3.0.

MWE:

#include <boost/detail/lightweight_test.hpp>
#include <boost/optional.hpp>

int main()
{
  boost::optional<int> a, b(1);
  BOOST_TEST(!a);
  BOOST_TEST(!!b);
  a = b;
  BOOST_TEST(!!a); // Fails on GCC 8 -std=c++98

  return boost::report_errors();
}

https://wandbox.org/permlink/UPpKB0gpchSAaW61

[Kojoley]

The problem goes away if I declare a copy assignment operator for tc_optional_base

    tc_optional_base& operator=( tc_optional_base const& rhs )
    {
        m_initialized = rhs.m_initialized;
        m_storage = rhs.m_storage;
        return *this;
    }

[Kojoley]

Hmm, it also goes away if I make this:

    void assign ( tc_optional_base const& rhs ) 
    {
      //this->operator=(rhs);
      *this = rhs;
    }

[Kojoley]

It looks like a GCC bug. MWE (fails on any -std):

struct dummy {} ;

template <typename T>
struct foo : dummy
{
    foo() {}
    foo(T v_) : v(v_) {}
    void assign(foo const& rhs)
    {
        this->operator=(rhs);     // the assignment does nothing
        //(*this).operator=(rhs); // this one does nothing too
        //*this = rhs;            // this one works as expected
    }

    T v;
};

template <typename T>
struct bar : foo<T>
{
    typedef foo<T> base;
    bar() : base() {}
    bar(T v) : base(v) {}
    bar& operator=(bar const& rhs)
    {
        this->assign( static_cast<base const&>(rhs) ) ;
        return *this ;
    }
};

int main()
{
    bar<int> a, b(123);
    a.assign(b);
    if (a.v != 123) throw "problem!";
}

If you remove inheriting from dummy or detemplatize the classes it will also solve the problem.

[Kojoley]

GCC bug report https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87531