[boost] Re: [Review] Named parameters library

From: Daniel Wallin (dalwan01_at_[hidden])
Date: 2004-11-13 12:17:57

Peter Dimov wrote:
[snip]
> Does the library support named constructor parameters, by 
> the way?

Yes, by creating forwarding constructors and delegating to some init
function.

   struct X
   {
       typedef keywords<...> init_kw;

       template<class A0>
       X(A0 const& a0)
       {
           init(init_kw(a0));
       }

       template<class A0, class A1>
       X(A0 const& a0, A1 const& a1)
       {
           init(init_kw(a0, a1));
       }

       .. etc ..

   private:
       template<class Args>
       void init(Args const& args)
       {
           ....
       }
   };

It's harder if you need to use initializer lists. I guess you can do:

   template<class A0>
   X(A0 const& a0)
       : x(init_kw(a0)[x | 0])
       , y(init_kw(a0)[y | 0])
   {
   }

   template<class A0, class A0>
   X(A0 const& a0, A1 const& a1)
       : x(init_kw(a0,a1)[x | 0])
       , y(init_kw(a0,a1)[y | 0])
   {
   }

Or add another level of inheritance to avoid repeating the extraction
and the defaults.

-- 
Daniel Wallin