[Boost-users] iterators

4 Oct 2003

      Hi,

I would like to raise a couple of points about the iterator adaptors.

Firstly, is it really necessary to have the predicate as part of the 
template specification for the filter_iterator? Surely it can be assumed 
that it will always be convertible to boost::function<bool (const 
value_type&)> ?

Secondly, by allowing the return type of the function used by the 
transform_iterator to be a reference can we not use it to implement a more 
generic form of indirect_iterator? The code below gives a flavour of the idea.

    struct dereference
    {
       typedef int result_type;

       int* data_;

       dereference(int* data):data_(data){}
       int operator()(int i) const { return data_[i]; }
    };

    int main()
    {
       int data[] = { 1,2,3,4,5,6,7,8 };
       int keys[] = { 0,3,1,6,5,4,2,7 };

       typedef boost::transform_iterator_generator<dereference, int*>::type 
indirect_iterator;

       indirect_iterator i(keys, dereference(data)), 
i_end(keys+8,dereference(data));

       while(i != i_end)
          std::cout << *i++ << ' ';

       return 0;
    }

    The output is:

    1 4 2 7 6 5 3 8

Witz