Re: [Boost-Users] Query regarding the use/limitiations of traits in metaprogramming

--- hicks wrote:

Query regarding the use/limitiations of traits in metaprogramming

I am trying to use traits pattern to assist in metaprogramming. I have the following problem.

A traits class "trait" defers a decision to another traits class "trait1" depending on the result of a third traits class "traita". However, the compiler does not cooperate. The code below excutes but gives unexpected output (also shown).

[Note:: The code has been reduced to the minimal to demonstrate the problem. I have a real task at hand not shown here.]

template <class T> struct traita { BOOST_STATIC_CONSTANT(int, value=0); }; template <> struct traita<int> { BOOST_STATIC_CONSTANT(int, value=1); };

template struct trait1 {};

template <class T> struct trait { BOOST_STATIC_CONSTANT(int, value=traita<T>::value); typedef trait1 t1; };

int main(int argc, char* argv[]) { std::cout << typeid(trait<int>::t1).name() << std::endl << trait<int>::value << std::endl ; return 0; }

output::

trait1 1

It would be nice if the first line of output were "trait1", but it isn't.

Any assistance would be greatly appreciated.

I have some questions for you: 1. Why are you so interested in the value of "typeid.name()"? 2. Are you sure this isn't a compiler problem? What compiler(s) have you tried this on? Noel __________________________________________________ Do You Yahoo!? Yahoo! Health - your guide to health and wellness http://health.yahoo.com