[v3] Fix libstdc++/54577

[Paolo Carlini]

Hi,

On 05/14/2013 03:41 PM, Jonathan Wakely wrote:
> I'd forgotten about the existence of __const_pointer_cast etc. in 
> <ext/cast.h> ...
Me too ;) I resorted to it as a sort of temporary kludge.
> I agree that in C++11 mode __normal_iterator::_M_const_cast should not 
> rely on the existence of a get() member on the custom pointer, because 
> that's not required to exist, and you can do it like this instead: 
> using PT = pointer_traits<ToType>; auto to = 
> PT::pointer_to(const_cast<PT::element_type&>(*from)); 
Indeed, I have something like this in my tree too.

Thanks!
Paolo.