Templating off of an arbitirary-length list of types in C++

Here's what I want to be able to type:

class foo : public watchKeys<A, B, C> {}; //Or any list of keys

Boost::mpl has sequences, which allow you to do this, but I don't want to have to do:

class foo : public watchKeys<mpl::list<A, B, C> > {};

I don't mind it being "ugly" or verbose on the inside, but I want the way watchKeys is ultimately used to be very simple and intuitive. I also can't figure out how boost is doing it, but that seems to be because there's a layer of macros between me and templates.

How might I go about this? I'd prefer not to do the giant list of templates for each number of types, bu开发者_运维知识库t if that's the only it's the only way...

Edit: I've become fairly certain that there's no way to do what I want to do (almost, but you can't have a variable number of macro arguments), but the question is still generating useful and informative answers.

The giant list of templates for each number of types is the only way to do it in the current version of C++. See boost::tuple for an example of how to go about.

C++0X supports variadic templates, but that isn't well supported yet (I think modern version of GCC have experimental support though).

Alternatively you can do it recursively

template<typename Head, typename Tail>
struct list { };

struct emptylist { };

class foo : public watchKeys<list<A, 
                             list<B, 
                             list<C, emptylist> > > > { };

You can then process it like this

template<typename List>
struct process;

template<typename Head, typename Tail>
struct process< list<Head, Tail> > : process<Tail> { 
  // process Head
};

template<>
struct process<emptylist> { };