The code using fusion::fold is elegant, but you still have to define a functor before using it. Couldn't boost just define a default hasher for tuple like the default comparison <boost/tuple/tuple_comparison.hpp>? I've got a tuple with 3 ints in it. I can compare them for free. Why can't I just hash them for free? All we'd have to do is define a hash_value function for tuple that calls fold.