Question

I want to able to pass two joined iterators as one to take advantage of some stl like algorithms (such as TBB) so I am making a custom iterator that joins them but am hitting some stumbling blocks.

I need to specialize iterator, however it won’t let me generically specify a template parameter.

Like so:

template<typename IT1, typename IT2>
struct multi_iter : public std::iterator<
                            std::output_iterator_tag,
                            std::pair<IT1::value_type&, IT2::value_type&> >
{
.
:

However it will let me do this, but this is not what I am after

template<typename IT1, typename IT2>
struct multi_iter : public std::iterator<
                            std::output_iterator_tag,
                            std::pair<int&, int&> >
{
.
:

I get this error

multi_iter.cpp:12:53: error: template argument 2 is invalid
multi_iter.cpp:12:55: error: template argument 2 is invalid
multi_iter.cpp:12:55: error: template argument 4 is invalid
multi_iter.cpp:12:55: error: template argument 5 is invalid
.
:

I do have the std::pair

Any help would be greatly appreciated.

Thanks

Answer 1

value_type is a dependent type on IT1, so you have to specify typename there

typename IT1::value_type