On Jun 24, 2008, at 7:07 AM, Daniel James wrote:
From the move semantics thread:
2008/6/24 David Abrahams <dave@boostpro.com>:
Daniel James wrote:
It mostly works. I've found two problems so far. Firstly, is_convertible didn't work for the type,
You found a bug in is_convertible?
I don't know if it's a bug. The example below fails to compile.
#include <boost/type_traits/is_convertible.hpp>
template <typename T> struct move_from {}; class Y { Y(Y& rhs); public: Y(move_from<Y>) {} };
bool const r = boost::is_convertible<move_from<Y>, Y>::value;
The tr1::is_convertible, which was born from boost::is_convertible, considers its "from" to be an lvalue when detecting convertibility. The C++0X std::is_convertible considers its "from" to be an rvalue when detecting convertibility. If one wants to restrict is_convertible to only consider lvalue froms, one simply specifies an lvalue reference: is_convertible<F&, T>::value (from is now considered as an lvalue). There is motivation for this change here: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2255.html (search for "is_convertible"). -Howard