{This is copy of a message on the developers list that needs attention from Boost.Optional Users} Hello people, A few days ago, a problem with Boot.Optional's assignment not properly handling aliasing scenarios (like self assignment) was pointed out. We concluded that the solution was to use T's operator=() directly instead of the Destroy+Construct pattern that I was using. I changed the code, tested it, and I was updating the documentation when I recalled the following long-standing issue: Currently, with the Destroy+Construct pattern, references are re-bound in case of assignment: int a = 123 ; int b = 456 ; int& ra = a ; int& rb = rb ; optional ora(ra); optional orb(rb); ora = orb ; // now 'ora' contains a reference to 'b' instead of 'a' b = 789 ; cout << *ora ; Prints 789 cout << a ; Prints 123 This is not the way assignment of reference types work in C++: ra = rb ; // The value of 'a' referenced by 'ra' is changed, not the reference itself. cout << a ; Prints 789 This error in the way optional treated assignment of reference types was pointed out by Joel de Guzman long ago when he started using Optional in Spirit. However, at the time, Joel explicitely asked me not to change this and keep the current rebinding semantics in order to minimize any impact in Spitit itself (which certainly has, o had, a much larger user base). If I change the code now to use T's operator=(), assignment of optional will have a _radically_ different semantics. A correct one, that's for sure, but end user code might be fundamentally impacted. Note: if you look at Optional documentation you will discover that assignment is only documented for T not being of reference type. This was intentional.. I left this undocumented becasue I knew back then that the current semantics were wrong but I couldn't fix it at the time because Spirit was (or could be) depending on it; yet I didn't want other users to depend on it as well... Of course, users could have "discovered" the (incorrect) semantics themselves and now rely on it, but I hope that the intentionally missing documentation served to keep the amount of users depending on this incorrect semantics very low. [At least it served _me_ to remember about this since I had forgotten] I really want to 'fix' this, i.e, give it correct semantics, so unless Joel or anyone else speaks now I'll move on, finish the documentation updates and commit the new version. Best, Fernando Cacciola P.S: Joel already agreed in the developers list that this needs to be fixed.