[Boost-users] [proto] transform for a templated proto::terminal type

Subject: [Boost-users] [proto] transform for a templated proto::terminal type
From: Manjunath Kudlur (keveman_at_[hidden])
Date: 2010-02-05 21:35:31

Hello,

I have some proto::terminal's as follows :

template<typename T>
struct Var {
  unsigned int id;
};

typedef proto::terminal<Var<int> >::type               int32_;
typedef proto::terminal<Var<float> >::type            float_;
typedef proto::terminal<Var<double> >::type       double_;

I can write a callable transform, with templated operator() functions
to handle each Var<> type as follows :

struct _var_tostr :
    proto::callable {

  typedef std::string result_type;

  template<typename T>
  result_type operator()(variables::Var<T> const &v) const {
    std::stringstream sout;
    sout << "S" << v.id;
    return sout.str();
  }

  template<typename T>
  result_type operator()(variables::VecVar<T> const &v) const {
    std::stringstream sout;
    sout << "V" << v.id;
    return sout.str();
  }

};

To activate the transform, I end up writing one rule for each Var<>
type as follows :

struct var_tostr :
    proto::or_<
    proto::when<proto::terminal<variables::Var<int> >,
_var_tostr(proto::_value)>
   ,proto::when<proto::terminal<variables::Var<float> >,
_var_tostr(proto::_value)>
   ,proto::when<proto::terminal<variables::Var<double> >,
_var_tostr(proto::_value)>
> {
};

This gets cumbersome when I have more Var<> types. Is there a way to
not list each Var<> type in the grammar? That is, I want to match any
Var<T> and just call the _var_tostr(proto::_value) transform. How can
I accomplish this?

Thanks,
Manjunath