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From: Howard Hinnant (hinnant_at_[hidden])
Date: 2005-12-17 12:37:45

On Dec 17, 2005, at 12:17 AM, Eric Niebler wrote:

> Here's my latest attempt. This works on gcc 3.4.4 (cygwin), but not on
> VC7.1 or (sadly) Comeau Online. Language lawyers, start your engines!
> template<typename T>
> struct probe
> {
> operator T ();
> operator T volatile const &() const;
> };
> template<typename T>
> probe<T> make_probe(T const &);
> template<typename T>
> char is_volatile(T const &);
> template<typename T>
> double is_volatile(T const volatile &);
> #define IS_RVALUE(x) \
> (\
> sizeof(char) == \
> sizeof(is_volatile(true?make_probe(x):(x)))\
> )

That's very cool!

Just as a thought experiment, I tried to re-implement your IS_RVALUE
macro in (what I hope to be) C++0X. My purpose was mainly just to
amuse myself, but also as a sanity check that C++0X will actually
make things like this easier. I'm aware that the motivation for
IS_RVALUE is also greatly reduced in C++0X. I'm just exploring.
Fwiw I came up with:

#include <type_traits>

template<typename T> T&& test(T&&);
#define IS_RVALUE(x) (std::is_rvalue_reference<decltype(test(x))

I only spent a couple of minutes on it, so I wouldn't take it to the
bank. But it is lightly tested.


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