On 08/20/2011 07:33 PM, Julian Gonggrijp wrote:
Pretty much. I think it could do the job. (Although of course it's not THE underlying type in a very strict conceptual sense.)
There is no such thing as an underlying type.
template<class T> void swap (T& x, T& y) { UNDERLYING_TYPE(T) temp; move_raw (x, temp); move_raw (y, x); move_raw (temp, y); }
This clearly looks like undefined behaviour.
It isn't. :-)
It is. This is not allowed outside of PODs. Also I assume move_raw here is memcpy. If it isn't, you have strict aliasing problems as well.
What I'm sure of, is that my library can (unintrusively) simulate move constructors, move destructors and the returning of rvalue references from functions. Of course, it doesn't use *only* bitwise copies for that purpose and the type involved needs to be default-constructible.
Why do you think it just cannot work?
Well it's pretty obvious that bitwise copy doesn't do the right thing in many cases. User-defined types can pretty much do whatever they want, and changing their address may very easy invalidate them. Some libraries have implemented standard-like containers like that. It is a known technique. It's just an utterly broken one.