assignment of boost::optional of const reference to a base works incorrectly

[yhirsch@…]

#include <iostream>
#include <boost/optional.hpp>

class B
{
public:

    virtual ~B() { }

    virtual void foo() const = 0;
};

class D : public B
{
public:

    virtual ~D() { std::cout << "D d-tor (" << this << ")" << std::endl; }
    D() { std::cout << "D default c-tor (" << this << ")" << std::endl; }
    D(const D& d) : B(d) { std::cout << "D copy c-tor (" << this << ")" << std::endl; }
    virtual void foo() const { std::cout << "D::foo (" << this << ")" << std::endl; }
};

int main(int argc, char** argv)
{
    D d;
    B& b = d;

    boost::optional<const B&> o;
    o = d;

    o->foo();
}

The above code compiles and crashes. The reason is the assignment o = d. Apparently, the assignment operator that gets called copies d (since it's passed by value), takes its reference and then the local copy gets destroyed, in which case o->foo() is called on an invalid object.

If the definition of o is changed to boost::optional<B&> the code doesn't compile (I haven't checked the whole code of boost::optional, but I assume this is intentional - in which case it should be the same in the const reference case).

Alternatively, assigning o = b instead of o = d works fine (because b is const B&) which is the same type as the template argument of the optional.

This was compiled on Fedora 14 x86_64, gcc 4.5.1 with boost 1.44.0.

[Steven Watanabe]

Duplicates #5303.