Ion Gaztañaga wrote:
For objects that have no such default-state, and have no resource reassignment functions (like reset() or similar) there is no problem because there is no interface to reuse the object.
I think I was with you until this point. It seems to me that the exact opposite is true; objects that have no "empty" or "default" state cannot implement a move, at least not easily, whereas reusing a moved-from object via assignment or reset is no problem at all. FWIW, I've changed the shared_ptr move constructors and assignment operators to leave the source empty, but this doesn't mean that I'm convinced that the general case needs to be constrained in such a way. In particular, T& operator=( T && r ) { swap( r ); return *this; } seems a very reasonable implementation of move assignment, and has a slight performance advantage (one call to ~T instead of two in a typical use case) over T& operator=( T && r ) { T( move( r ) ).swap( *this ); return *this; } which is what is needed for r to be left empty.