No I think evan got it right. constrain as less as possible. you can constrain more later if you need to.
STL needs a crystalline/congealed interface. you can't inspect running sources, insert prints. all you have are compiler errors and API docs. we dont have those constraints, let's not tether ourselves to libs. libs and APIs are for more static languages. we don't need a new configuration of sources to just work. let's back off. just tell me the moment something fails.