Why doesn't boost::fusion::as_set remove duplicates from a boost::fusion::vector?

Question

I have:

auto my_vec2 = boost::fusion::make_vector(42,false,42);
auto my_set2 = boost::fusion::as_set(my_vec2);

and when I go to debug I was expecting my_set2 to only contain 42 and false, however it contained 42 twice. Why is this? If its a set surely the "keys" should be unique?

Answer 1

It’s your responsibility:

Precondition: There may be no duplicate key types.

(from this doc)