Given this class:

class C
{
    private:
        struct Foo
        {
            int key1, key2, value;
        };
        std::vector<Foo> fooList;
};

The idea here is that fooList can be indexed by either key1 or key2 of the Foo struct. I'm trying to write functors to pass to std::find so I can look up items in fooList by each key. But I can't get them to compile because Foo is private within the class (it's not part of C's interface). Is there a way to do this without exposing Foo to the rest of the world?

(note: I've got to run to a meeting. I'll be able to post more sample code in about a half hour.)