[Boost-bugs] [Boost C++ Libraries] #5303: assignment of boost::optional of const reference to a base works incorrectly

Subject: [Boost-bugs] [Boost C++ Libraries] #5303: assignment of boost::optional of const reference to a base works incorrectly
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-03-14 06:42:11

#5303: assignment of boost::optional of const reference to a base works
incorrectly
--------------------------------------+-------------------------------------
 Reporter:  yhirsch@…                 |       Owner:  fcacciola
     Type:  Bugs                      |      Status:  new      
Milestone:  To Be Determined          |   Component:  optional 
  Version:  Boost 1.44.0              |    Severity:  Problem  
 Keywords:                            |  
--------------------------------------+-------------------------------------
 {{{
 #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.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5303>
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