Re: [boost] Boost.Lambda

From: Brian McNamara (lorgon_at_[hidden])
Date: 2004-04-29 15:15:38

On Thu, Apr 29, 2004 at 10:05:19PM +0300, Justinas V.D. wrote:
> The problem is that lambda expressions do not have result_type defined 
> although technically they are functors too (like STL functors). It would 
> be trivial to write little metafunction wrapper though. After all, 
> boost::lambda::is_lambda_functor metafunction exists but I haven't found 
> lambda_result_type traits or something like that. Documentation 
> conveniently skips through that part of implementation and code is a bit 
> obscure at times.
> 
> Is there a way to implement such a metafunction
> 
>    boost::lambda::functor_result<T>::type that it would return result 
> type of lambda expression if T is lambda
>    expression or T::result_type if T is ordinary STL functor, or just 
> null_type if neither of them?
> 
> that its implementation would not turn out to be a pain in the... emm... 
> neck? Or perhaps this could be a part of Boost.Lambda library?

I think what you want is result_of.

   http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1454.html

Last I heard, a complete implementation had not yet made it into Boost.
Douglas?  I think maybe Boost.Lambda already has the implementation
support for it, we just need the main result_of interface.

To Douglas: I am starting to have a little free time again, so if you
want help implementing it or making some tests, I will help here.  

-- 
-Brian McNamara (lorgon_at_[hidden])