Result returning constructors

An oft-asked question during conference talks on Expected/Outcome is how to exclusively use result to implement constructor failure. This is asked because whilst almost every member function in a class can return a result, constructors do not return values and thus cannot return a result. The implication is that one cannot avoid throwing C++ exceptions to abort a construction.

As with most things in C++, one can achieve zero-exception-throw object construction using a lot of extra typing of boilerplate, and a little bit of simple C++ metaprogramming. This section shows you how to implement these for those who are absolutely adverse to ever throwing an exception, or cannot because C++ exceptions have been globally disabled.

The technique described here is not suitable for non-copyable and non-movable types. There is also an assumption that moving your type is cheap.