Hello, The current implementation of boost::noncopyable prevents derived classes from declaring a defaulted move constructor: #include <boost/noncopyable.hpp> struct S : boost::noncopyable { S(S&&) = default; }; S f(); int main() { S s = f(); } Errors (with gcc trunk): test3.cpp: In function 'int main()': test3.cpp:12:13: error: use of deleted function 'S::S(S&&)' test3.cpp:5:5: error: 'S::S(S&&)' is implicitly deleted because the default definition would be ill-formed: /usr/include/boost/noncopyable.hpp:27:7: error: 'boost::noncopyable_::noncopyable::noncopyable(const boost::noncopyable_::noncopyable&)' is private test3.cpp:5:5: error: within this context The problem is that the default move constructor for S tries to move the noncopyable base subobject, but noncopyable does not have a move constructor (one isn't generated implicitly because a user-defined copy constructor is present). Then it tries to fall back to the noncopyable copy constructor, but that of course is private. If we give the definition of the S move constructor explicitly, all is well because no one is trying to move or copy the noncopyable subobject: struct S : boost::noncopyable { S(S&&) {} }; However, having to define the move constructor explicitly is annoying and a maintenance hazard (e.g. if you add a data member, you have to add it to the move constructor too). If we modify noncopyable to give it a move constructor, the defaulted move constructor now works in derived classes. I think we should either give noncopyable a move constructor, or add a similar class ("noncopyable_but_movable"? - I'm bad with names) that is like noncopyable but also has a move constructor. Thoughts? Regards, Nate.