Re: [Boost-users] Template instantiation function arguments and Boost.Preprocessor

From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2008-01-28 16:39:09

AMDG

Hicham Mouline wrote:
> After some though, here is more precisely what I'd like to have...
> I apologize that it is quite different from the initial problem:
>
> template<int n> class Tree {
>   static double sum();  // 
> };
>
>
> If the user instantiates tree<2>, he should get:
>
> template<> class Tree<2> {
>   static double sum(double d1, double d2);
> };
>
> template<> class Tree<3> {
>   static double sum(double d1, double d2, double d3);
> };
> etc etc...
>
>
> so that in user code, for e.g.:
>
>   double d= Tree<4>::sum(d1, d2, d3, d4);
>
> should compile.
>
>
> Is it possible for me to just define the template Tree for the n-case
> without the 2- and 3- specializations?
>   

Ah.  You still need the preprocessor, but you can rearrange the 
definitions slightly.
(untested)

template<int N>
struct TreeSumImpl;

#define TREE_SUM_DEF(z, n, data)\
    template<>\
    struct TreeSumImpl<n> {\
        static double sum(BOOST_PP_ENUM_PARAMS_Z(z, n, double arg)) { ... }\
    };

BOOST_PP_REPEAT(20, TREE_SUM_DEF, ~)

template<int N>
struct Tree : TreeSumImpl<N> {
    // other code
};

In Christ,
Steven Watanabe