reverse_fold has no static assert for requiring bidirectional sequence

[Kojoley]

The example from documentation https://www.boost.org/doc/libs/1_69_0/libs/fusion/doc/html/fusion/algorithm/iteration/functions/reverse_fold.html compiles fine as-is, but replacing vector with cons yield a compile error. This seems to be a regression, because I came to it at debugging failure in Proto tests, but it might be introduced a long time ago.

Update: the Proto test/example is simply violating Fusion invariants. I opened a PR to fix it boostorg/proto#15.

[Kojoley]

It turns out that Fusion is fine, reverse_fold requires a Bidirectional Sequence while cons is a Forward Sequence, though it could have a static assert like reverse_view has

fusion/include/boost/fusion/view/reverse_view/reverse_view.hpp

Lines 48 to 51 in afb8b15

	BOOST_STATIC_ASSERT((
	is_base_of<
	bidirectional_traversal_tag
	, typename traits::category_of<first_type>::type>::value));