[boost] [boost::proto] how to get the type of a proto expression?

From: Maurizio Vitale (mav_at_[hidden])
Date: 2007-05-07 20:47:21

Eric,
        I can get the type of a proto expression (wrapped in a user-defined skin) using
BOOST_TYPEOF, but then I noticed BOOST_PROTO_TYPEOF in context.hpp.

Which one is supposed to be used?

BOOST_PROTO_TYPEOF fails on me when trying to emulate the way it is used inside context.hpp.

Here is code that shows what I'm trying. If BOOST_PROTO_TYPEOF is internal only, just let me know and forget
the code below.

Regards,

        Maurizio

#include <iostream>

#define BOOST_MPL_CFG_NO_PREPROCESSED_HEADERS
#define BOOST_PROTO_MAX_ARITY 8
#define BOOST_MPL_LIMIT_METAFUNCTION_ARITY 8                // GCC bug workaround, needs to be at least BOOST_PROTO_MAX_ARITY

#include <boost/xpressive/proto/proto.hpp>
#include <boost/xpressive/proto/context.hpp>
#include <boost/xpressive/proto/extends.hpp>
#include <boost/xpressive/proto/transform/arg.hpp>
#include <boost/xpressive/proto/transform/construct.hpp>

namespace proto=boost::proto;
namespace mpl=boost::mpl;
using proto::_;

struct my_domain : proto::domain<struct my_grammar> {};
//struct my_domain : proto::domain<> {};

template<typename> struct my_context;

template <typename Expr>
struct my_expr : proto::extends<Expr, my_expr<Expr>, my_domain> {
  typedef proto::extends<Expr, my_expr<Expr>, my_domain> base_type;

  my_expr (Expr const& expr = Expr()) : base_type (expr) {};

  using base_type::operator =;

  operator int () const {
    return static_cast<int>(proto::eval(*this, my_context<Expr> ()));
  }

  operator unsigned int () const {
    return static_cast<unsigned int>(proto::eval(*this, my_context<Expr> ()));
  }
};

template<typename A, typename B, typename C, typename D, typename E, typename F, typename G, typename H> 
struct number {
  unsigned int m_data;
};

struct my_grammar : proto::or_ <
  proto::terminal< number<_,_,_,_,_,_,_,_>  > ,
  proto::terminal<int>,
  proto::terminal<unsigned int>,
  proto::unary_expr<proto::_, my_grammar> ,                       
  proto::binary_expr<proto::_, my_grammar, my_grammar> 
  >
{};

namespace boost { namespace proto {
  template<typename Expr>
  struct generate<my_domain, Expr> {
    typedef my_expr<Expr> type;
      
    static type make (Expr const& expr) {
      return type (expr);
    }
  };
} } 				// end namespace boost::proto

template<typename Expr>
struct my_context : proto::callable_context<const my_context<Expr> > {
  typedef unsigned int result_type;

  template<typename A, typename B, typename C, typename D, typename E, typename F, typename G, typename H> 
  unsigned int operator () (proto::tag::terminal, number<A,B,C,D,E,F,G,H>  n) const { return n.m_data; }
};

template<int N>
struct my_int : my_expr<typename proto::terminal< number<mpl::int_<0>,mpl::int_<0>, mpl::int_<0>, mpl::int_<0>, mpl::int_<0>, mpl::int_<0>, mpl::int_<0>, mpl::int_<0> >  >::type>
{
  typedef number<mpl::int_<0>,mpl::int_<0>, mpl::int_<0>, mpl::int_<0>, mpl::int_<0>, mpl::int_<0>, mpl::int_<0>, mpl::int_<0> >  number_type;
  typedef my_expr<typename proto::terminal<number_type>::type> expr_type;

  my_int () {}
  my_int (int i) : expr_type (expr_type::type::make (i)) {}

  template<typename Expr>
  my_int& operator = (const my_expr<Expr>& e) {
    proto::arg (*this).m_data = static_cast<int>(proto::eval(e, my_context<Expr> ()));
    return *this;
  }

  template<typename T>
  my_int& operator = (T value) {
    proto::arg (*this).m_data = value;
    return *this;
  }
};

template<typename T> struct dump;
#define DUMP(T) typedef dump<T>::type t

int main (int,char**) {
  my_int<6> i4(-22);

  int i;
  unsigned int j;

  i4 = 5;
  i4 = 5*i4;

  i = i4/i4+4;
  j = i4/i4;

  BOOST_PROTO_TYPEOF (i4+j+2, a_type);
  DUMP (a_type);
  
//  typedef BOOST_TYPEOF (i4*2) another_type;
//  DUMP(another_type);
}


/// Local Variables:
/// mode:c++
/// comment-column:80
/// fill-column:160
/// compilation-read-command:nil
/// compile-command:"g++ -I. -ope1 pe1.cpp"
/// End: