Thanks! I knew something like could be written, but for some reason I thought there'd be significantly more overhead in turning a function into something loopable. It's unfortunate that one can't pass a function template as a template argument, since that would remove the need for the extra functor class entirely. Geoffrey On Fri, Aug 26, 2005 at 04:24:36PM -0500, Alan M. Carroll wrote:
Here's some code I whipped out that does what you want, although I'm sure it could be done better (it was an interesting learning exercise, though)
# include <boost/mpl/if.hpp> # include <boost/mpl/list.hpp> # include <boost/mpl/empty.hpp> # include <boost/mpl/front.hpp> # include <boost/mpl/pop_front.hpp>
// this is the thing we want to call on the types // We don't put it in the functor so that it can be specialized in multiple places template < typename T > void complicated_function( int i) { std::cout << "i = " << i << " sizeof = " << sizeof (T) << std::endl; }
// need this as a simple type so we can pass it to chain struct functor { template < typename T > void operator () (int i) const { complicated_function<T>(i); } };
// do tail recursion on L using the functor F template < typename F , typename L > struct chain { struct tail { void operator () (int i) const { return ; } }; struct main { void operator () (int i) const { F f; f. operator ()<boost::mpl::front<L>::type >(i); chain<F, boost::mpl::pop_front<L>::type>()(i); } }; void operator () (int i) const { boost::mpl::if_c<boost::mpl::empty<L>::value, tail, main >::type ()(i); } };
// A list of types to use typedef boost::mpl::list< int, double , char , std::string> the_list;
// demonstrate that we're calling complicated_function for each type in the list void mpl_test() { chain<functor, the_list>()(17); }