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

28 Jan 2008

      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