Using an object after std::move doesn't result in a compilation error

Question

After std::move is called on an object, why doesn't the language cause a compilation error if the object is used after?

Is it because it is not possible for compiler to detect this condition?

Answer 1

The general principle in C++ language design is "trust the programmer". Some issues I can think of with rejecting any use of the object after it has been an argument to std::move.

• To determine whether a given use is after a call to std::move in the general case would be equivalent to solving the halting problem. (In other words, it can't be done.) You would have to come up with some rules that describe what you mean by "after" in a way that can be statically determined.
• In general, it is perfectly safe to assign to an object that has been an argument to std::move. (A particular class might cause an assertion, but that would be a very odd design.)
• It's hard for a compiler to tell whether a given function is going to just assign the elements of the class new values.