Re: Another approach to forward/move issues
On Mar 5, 3:12 pm, "W Karas" <wka...@yahoo.com> wrote:
On Feb 20, 12:38 pm, "W Karas" <wka...@yahoo.com> wrote:
Add this ?pseudo? class template
to the std namespace:
template <typename T>
class rvalue;
For any type X, the types X and rvalue<X>
would be distinct but have exactly the
same interface/size/alignment. For
value/reference/pointer conversion, both
would convert to ?const X? implicitly, but
conversion between them would require a static cast.
Anonymous, compiler-generated temporary instances
(r-values) would be of type rvalue<X>. This seems
to solve the forwarding problem, because
template type deduction would capture the
difference between a const reference and a
temporary (without changes to the deduction
rules).
A named instance of rvalue<X> would save one cast
in a swap:
std::rvalue<X> t = static_cast<std::rvalue<X> &>(a);
a = static_cast<std::rvalue<X> &>(b);
b = t;
It would be nice, if you could explain your reasons,
why your proposed class template rvalue is better
than the current rvalue proposal? The most recent
document is here:
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2118.html
This one corresponds to the primary proposal:
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1690.html
and these are some intermediates, which explain also library
impact:
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1770.html
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1771.html
At the cost of adding a new reserve word, "rvalue" could
become a type modifier like "const" and "volatile".
This seems more intuitive, and presents an obvious
solution to how to declare member functions where
the instance itself is expected to be an rvalue:
void foo(void) rvalue;
analogous to:
void foo(void) const;
What is the advantage of an rvalue-function foo? What should
it do that should not be done for const, volatile, or not-cv-not-
rvalue
types?
The rvalue proposal allow selected member functions to support
move-semantic, e.g.
struct C {
C(C&& rhs);
void swap(C&& other);
};
Isn't this sufficient?
Greetings from Bremen,
Daniel Kr?gler
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