Re: [boost] Re: Policy-based vector? [was: Submission: Fixed-Capacity STL Containers Library]

From: Beman Dawes (bdawes_at_[hidden])
Date: 2002-02-06 20:15:09

At 02:50 PM 2/6/2002, Jeremy Siek wrote:
 >
 >The closest we can currently come to a templated typedef is to use a type
 >generator.
 >
 >template <typename A, typename B>
 >struct generic {
 >  A a;
 >  B b;
 >};
 >
 >// Can't do this
 >//template <typename A>
 >//typedef generic<A, int> specific;
 >//
 >// then usage is:  specific<A>
 >
 >template <typename A>
 >struct specific { typedef generic<A,int> type; };
 >
 >// then usage is:   typename specific<A>::type
 >
 >Personally, I don't find type generators all that bad. I'd be happy with
 >using them all over the place until we get templated typedefs into the
 >language. Do other people feel differently?

What is wrong with forwarding classes (until typedef templates make it into 
the language)?

   template <typename T>
   struct specific_a : public generic<T, policy_a>
     { ... forwarding ctors, etc. };

   template <typename T>
   struct specific_b : public generic<T, policy_b>
     { ... forwarding ctors, etc. };

At the cost of having to write and maintain more code, doesn't the above 
simulate:

   template <typename T>
   typedef generic<T, policy_a> specific_a;

   template <typename T>
   typedef generic<T, policy_b> specific_b;

Or am I missing something?

--Beman