Re: [Boost-users] Converting loop to using boost::lambda where containers has boost::shared_ptrs

21 May 2007

      Alright, I solved it. Two small changes in the code did it. Hope they
are not too bad for you.

First I needed to remove the =0 statement for the to_string in your
base class. If I don't do that I can the following error:

c:\boost_1_34_0\boost\tuple\detail\tuple_basic.hpp(328) : error C2259:
'Base' : cannot instantiate abstract class
[snip]

So my base class looks like as follows:

class Base {
public:

   virtual std::string to_String ( boost::uint32_t indent )
   { return "" ;}
};

Second change was to remove the boost::bind lib and to use lambda's
bind. I also needed to add an asterisk to _1.

Here is the complete code that works on my machine.

#include <string>
#include <sstream>
#include <boost/cstdint.hpp>
#include <vector>
#include <boost/shared_ptr.hpp>
#include <boost/lambda/lambda.hpp>
#include <boost/lambda/bind.hpp>
#include <iostream>

using namespace boost::lambda;

class Base {
public:

   virtual std::string to_String ( boost::uint32_t indent )
   { return "" ;}
};

class A : public Base {
public:

   A ( boost::uint32_t value )
       : m_value ( value )
   {}

   virtual std::string to_String ( boost::uint32_t indent )
   {
       std::stringstream output;

       for ( boost::uint32_t i = 0; i < indent; i++ )
           {
               output << " ";
           }

       output << m_value;

       return output.str();
   }

private:

   boost::uint32_t m_value;
};

class D : public Base {
public:

   D ( boost::uint32_t value )
       : m_value ( value )
   {}

   virtual std::string to_String ( boost::uint32_t indent )
   {
       std::stringstream output;

       for ( boost::uint32_t i = 0; i < indent; i++ )
           {
               output << " ";
           }

       output << m_value;

       return output.str();
   }

private:

   boost::uint32_t m_value;
};

const char* print( const std::string& s )
{
   return s.c_str();
}

int main ( int, char** )
{
   typedef boost::shared_ptr<A> A_ptr_t;
   typedef boost::shared_ptr<D> D_ptr_t;

   typedef std::vector < boost::shared_ptr<Base> > Data_t;
   Data_t m_data;

   A_ptr_t a ( new A ( 50 ) );
   D_ptr_t d ( new D ( 30 ) );

   m_data.push_back ( a );
   m_data.push_back ( d );

   boost::uint32_t indent_value = 4;

   std::for_each ( m_data.begin(),
                   m_data.end(),
                   std::cout << bind( &Base::to_String,
                                              *_1,
                                              indent_value ) );
   return 0;
}

Regards,
Christian

Re: [Boost-users] Converting loop to using boost::lambda where containers has boost::shared_ptrs

Christian Henning