[Boost-users] [proto] Object got sliced when passed by reference

Subject: [Boost-users] [proto] Object got sliced when passed by reference
From: Leon Sit (wing1127aishi_at_[hidden])
Date: 2011-03-11 16:57:04

Hi all

I have a class tree as the following

template<typename T>
struct base{
  bool operator()(int i)const {
    return static_cast< const T&>(*this)(i);
  }
};
struct F1:public base<F1>{
  bool operator()(int i) const{
    return true;
  }
};
struct F2:public base<F2>{
  bool operator()(int i) const{
    return true;
  }
};
struct F3 :public base<F3>{
  std::string junk_;
  F3(std::string junk):junk_(junk){}
  bool operator()(int i) const{
    std::cout << junk_ << std::endl;
    return false;
  }
};

==================================================================

I am trying to use proto to derive the following systax

Predicate<F1> f1;
Predicate<F2> f2;
Predicate<F3> f3("hodqhoqw");

cout << ((f1||f2)&&f3)(1) << endl;

==================================================================

When proto get to the point of invoking the F3::operator(), the junk_
attribute got sliced away. I thought I am passing everything by constant
reference but the exception tells me otherwise. The full sample code is
attached, can someone tell me what I have missed? I am testing my code on
vc9 and vc10, and I am not using virtual function for performance issue.

Ultimately, I want to have the following syntax in the client code

F1 f1;
F2 f2;
F3 f3("hodqhoqw");

cout << ((f1||f2)&&f3)(1) << endl;

Thanks