Programming

To sum up the main problem: Modern C++ does not implement destructive moves that are checked at compile time. Instead, moving from an object needs to take into account that it can potentially be used again, because in C++ it does not become destroyed or inaccessible as result of the move.

This requires to set some objects - especially ones that track resources in an exclusive way - to an invalid or uninitialized state. For example, collections can be set to an empty collection, which is a valid state that frees resources. But a thread class would have an invalid thread id, and a unique smart pointer class a null pointer or a "deleted" flag, both of which need to be checked at run time.

And this would be less of a problem if it were not a core promise if C++ that, by virtue of its constructors, any object that has successfully been constructed, is in a valid state (or never came into existence). (And the latter requires, of course, using exceptions and RAII, which in turn requires most code to be exception-safe, which, considering the many possibilities for UB to occur, is less trivial than it might sound...).