-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Ion Gaztañaga Sent: Monday, April 16, 2007 10:33 AM To: boost@lists.boost.org Subject: Re: [boost] [shared_ptr] dangerous implementation of moveconstructor
std::vector<T> myvect(...); //myvect's destructor is called, the object is not longer usable std::vector<T> myvect2(std::destructive_move(myvect)); myvect.resize(1000); <-- COMPILATION ERROR
That pretty much goes against normal C++ scoping rules (theyre not related here but from a readability pov, they are) and would be very confusing. In this code here: if(some_runtime_condition) { ...std::destructive_move(myvect)... } ... if(!some_runtime_condition && some_other_runtime_condition) { use_myvect(myvect); } It isn't easy for the compiler to help you. Well defined and standard-mandated semantics are better in the long run, even if its possible for the case you had above not be an error (should be a warning though!). The rule should be simple: After moving, the moved object (i.e., the argument to std::move) should be destructible. I don't think being assignable makes sense because that implies that a default constructor is sensible for T. I can imagine this is more intuitive C++ and is easier for compilers to implement. Thanks for listening (and discussing this very important topic!) Sohail