Using of rvalue references in c++11

Question

I would like to implement a function that fills up a vector and then returns an rvalue reference. I tired something like:

std::vector &&fi         


        

Answer 1

The return statement is an error because you atempt to bind an rvalue reference (the return type) to an lvalue (the vector res). An rvalue reference can only be bound to an rvalue.

Also, as others already mentioned, returning a local variable when the return type is a reference type is dangerous, because the local object will be destroyed after the return statement, then you get a reference that refers to an invalid object.

If you want to avoid the copy construction during the return statement, just using a non-reference type might already works due to a feature called copy elision. the vector res in your fill_list function may be directly constructed into the vector myvec in your main function, so no copy or move construction is invoked at all. But this feature is allowed by Standard not required, some copy construction is not omitted in some compiler.