> For example suppose that I have a class that has reference members. Those are fields specified with & - they are kind of like a pointer except that you can't change them, and you use . instead of ->. Because you can't change them, operator= is not generated for you. I didn't notice this until I tried to use one in an std::map< ... > and everything blew up.
This is what std::reference_wrapper is for.
> I don't care what kind of data structure this came from
This is what std::reference_wrapper is for.
> I don't care what kind of data structure this came from
Fortunately, neither does the STL.
for_each(begin(foo_container), end(foo_container), some_foo_op);
Do you know what kind of container foo_container is? It doesn't matter. It can be a set, vector, list, or even a plain array.
> And then you can dream up things like the ability to take an iterator< foo > and a method on foo that will return a bar, to get an iterator< bar >
You can do this with std::transform.
transform(begin(foo_container), end(foo_container), begin(bar_container), op_to_make_foo_into_bar);
edit: I see from your other response that what you actually want is streams or generators, not an iterator.