Question

I’d like to use the boost::transform_iterator together with boost::bind to return the result of a member function.

e.g.

class Foo
{
public:
//...
Bar& getBar();
const Bar& getBar() const;
};

I’ve got a unary Function object to select the getBar() function

struct getBar: public std::unary_function<Foo&,Bar&>
{
  getBar::result_type operator()(getBar::argument_type arg ) const {
    return arg.getBar()
  }
};

and lets say i’ve stored several Foo objects inside a std::vector and Im using a tranform_iterator like that

int main()
{
  typedef std::vector<Foo> VEC;
  typedef boost::transform_iterator<getBar,VEC::iterator> iterator;
  VEC vec;
  vec.push_back( Foo ());
  iterator i( vec.begin() );
  //...
  Bar = *i;
  return 0;
};

But if i want to use boost::bind instead of the getBar functor how would i do that. I’m not sure which template parameter I would have to pass to the transform_iterator.

EDIT:

the solution with boost::function was a good start but i wasn’t completely satisfied so experimented a bit and looked into the return type of boost::mem_fn

typedef boost::transform_iterator<boost::_mfi::mf0<Bar&,Foo>,VEC::iterator> iter;
typedef boost::transform_iterator<boost::_mfi::cmf0<const Bar&,Foo>,VEC::const_iterator> citer;

but this solution has another problem.
because

iter i(v.begin(), boost::mem_fn( &Foo::getBar ));
citer ci(v.begin(), boost::mem_fn( &Foo::getBar ));

leads to the following error

call of overloaded mem_fn(<unresolved overloaded function type>) is ambiguous

the compiler is not able to identify which getBar function is requested and I had to help him a little.

iter i(v.begin(), boost::mem_fn( static_cast<Bar& (Foo::*)()>(&Foo::getBar) ));
citer ci(v.begin(), boost::mem_fn( static_cast<const Bar& (Foo::*)() const >(&Foo::getBar) ));

this is probably not faster than writing a little functor by hand but at least it helped me to understand boost::mem_fn a bit more.

Answer 1

boost::transform_iterator<boost::function<Bar&(Foo&)>,std::vector<Foo>::iterator>