===================================== MODERATOR'S COMMENT:
 Please don't overquote.


===================================== END OF MODERATOR'S COMMENT
google@dalvander.com (Anders Dalvander) wrote in message news:<d04c84a9.0305080931.609ce9a2@posting.google.com>...
> Take a look at http://www.boost.org/libs/type_traits/index.htm (Boost
> - Type Traits), and see how they have solved it.
>
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I did, but I still want to know why my way of doing it doesn't get the
results I expected.

Robert

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notbob@tessellation.com (Robert Allan Schwartz) wrote:
[...]
> I did, but I still want to know why my way of doing it doesn't get the
> results I expected.

I think it's a GNU C++ 3.2 bug.  At least on MacOS X,
it gives suspicious warnings about ignoring the
volatile qualifiers while instantiating is_volatile
(apparently, it finds the partial specialization an
acceptable match).

        Daveed

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Robert Allan Schwartz wrote:
> google@dalvander.com (Anders Dalvander) wrote in message
>> Take a look at http://www.boost.org/libs/type_traits/index.htm (Boost
>> - Type Traits), and see how they have solved it.
>
> I did, but I still want to know why my way of doing it doesn't get the
> results I expected.

Most likely, for the same reason your is_const didn't work as expected:
compiler bugs.  The developers of boost:type_traits have spent a great deal
of time finding techniques that work on a wide variety of compilers.  That
may involve using a more complex yet still standard-conforming construct
(which the compilers happen to translate correctly), or it may involve
illegal constructs (which the compilers happen to translate into code with
the desired meaning despite it's being illegal).  (Caveat:  I haven't
studied boost:type_traits, so I don't know if any technically illegal code
is used - it's only supposition on my part that it might be the case).

-cd



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The program:

template <typename T>
class is_volatile { public: static const bool value = false; };

template <typename T>
class is_volatile<volatile T> { public: static const bool value = true; };

#include <iostream>

int main()
{
 std::cout << "is_volatile<bool &>::value = " << is_volatile<bool &>::value
<< std::endl;

 std::cout << "is_volatile<void (void)>::value = " << is_volatile<void
(void)>::value << std::endl;
 std::cout << "is_volatile<int  (void)>::value = " << is_volatile<int
(void)>::value << std::endl;
 std::cout << "is_volatile<int  (int )>::value = " << is_volatile<int  (int
)>::value << std::endl;

 return 0;
}

gives the results:

is_volatile<bool &>::value = 1
is_volatile<void (void)>::value = 1
is_volatile<int  (void)>::value = 1
is_volatile<int  (int )>::value = 1

on g++ v3.2, but gives the results:

is_volatile<bool &>::value = 0
is_volatile<void (void)>::value = 0
is_volatile<int  (void)>::value = 0
is_volatile<int  (int )>::value = 0

on metrowerks v7.

I believe the answers should all be 0.

What does the standard say?

Thank you,

Robert Schwartz

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Take a look at http://www.boost.org/libs/type_traits/index.htm (Boost
- Type Traits), and see how they have solved it.

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