[boost] [Container] small flat set ?

Dear all, boost::container::small_vector and boost::container::static_vector are great. boost::container::flat_set is great too. But today I need a small_flat_set! And I don't think it's possible to compose flat_set and small_vector. (flat_set can use a custom allocator, but it can't take a custom implementation type in the way that, for example, std::priority_queue can.) Having said that, maybe composing flat_set and small_vector (or static_vector) isn't the optimum solution for the case where I will store something like 0...4 ints; I suspect that linear search in an unordered sequence will be quicker. But that gets complicated if you need iterators with the normal behaviour. Any thoughts? Regards, Phil.