c++ boost::any to define my own print ,

Question

Am struggling a lot to find how to do to use boost::any to create a print function that can print any type using template first.

template 

        

Answer 1

There is quite easy way to do this, described in "Beyond the C++ Standard Library: An Introduction to Boost":

struct streamer {
  virtual void print(ostream &o, const boost::any &a) const =0;
  virtual streamer * clone() const = 0;
  virtual ~streamer() {}
};

template 
struct streamer_impl: streamer{
  void print(ostream &o, const boost::any &a) const { o << *boost::any_cast(a); }
  streamer *clone() const { return new streamer_impl(); }
};

class any_out {
  streamer *streamer_;
  boost::any o_;
  void swap(any_out & r){
    std::swap(streamer_, r.streamer_);
    std::swap(o_, r.o_);
  }
public:
  any_out(): streamer_(0) {}
  template any_out(const T& value)
    : streamer_(new streamer_impl()), o_(value) {}
  any_out(const any_out& a)
    : streamer_(a.streamer_ ? a.streamer_->clone() : 0), o_(a.o_) {}

  template 
  any_out & operator=(const T& r) { 
    any_out(r).swap(*this);
    return *this;
  }
  ~any_out() { delete streamer_; }

  friend std::ostream &operator<<(std::ostream& o, const any_out & a) {
    if(a.streamer_)
      a.streamer_->print(o, a);
    return o;
  }
};

and then you use any_out instead of boost::any.