Container of shared_ptr's but iterate with raw pointers

c++, iterator

Solution

Here's an option using Boost transform_iterator:

#include <list>
#include <boost/iterator/transform_iterator.hpp>
#include <tr1/memory>
#include <tr1/functional>

using std::list;
using std::tr1::shared_ptr;
using boost::transform_iterator;
using boost::make_transform_iterator;
using std::tr1::mem_fn;
using std::tr1::function;

struct Foo {};

struct Bar
{
  typedef shared_ptr< Foo > Ptr;
  typedef list< Ptr > List;
  typedef function< Foo* (Ptr) > Functor;
  typedef transform_iterator< Functor, List::iterator > Iterator;

  Iterator begin()
  {
    return make_transform_iterator( fooptrs.begin(), mem_fn( &Ptr::get ) );
  }

  Iterator end()
  {
    return make_transform_iterator( fooptrs.end(), mem_fn( &Ptr::get ) );
  }

  List fooptrs;
};

C++11 would make it easy to eliminate the `function` wrapper but I don't have a compiler handy to test it out. You could also hide the concrete type of `Iterator` using type-erasure if you saw the need (I think Adobe offers a free `any_iterator` class template for this purpose.)

Problem

I have a class that holds a list containing `boost::shared_ptrs` to objects of another class. The class member functions that give access to the elemets in the list return raw pointers. For consistency I'd also like to be able to iterate with raw pointers instead of shared_ptrs. So when I dereference the list iterator, I'd like to get raw pointer, not a `shared_ptr`. I assume I need to write a custom iterator for this. Is this correct? If so can someone point me in the right direction - I've never done this before.

Original source