Question

In C++03 it is impossible to return an object of a class having a private non-defined copy constructor by value:

struct A { A(int x) { ... } private: A(A const&); };

A f() {
  return A(10); // error!
  return 10;    // error too!
}

I was wondering, was this restriction lifted in C++11, making it possible to write functions having a class type return type for classes without constructors used for copy or move? I remember it could be useful to allow callers of a function use the newly returned object, but that they are not able to copy the value and store it somewhere.

Answer 1

Here is how it can work

A f() {
  return { 10 };
}

This works even though A has no working copy or move constructor and no other constructor that could copy or move an A!

To make use of this feature of C++11, the constructor (taking int in this case) has to be non-explicit though.