I'm not sure I follow? Does rust not have the equivalent of a LinkedHashMap from Java? All I'm proposing is to start each map of headers off with a sentinel value for all of the headers you don't intend to send back to the client. Then, have a method that iterates over all values, for the places you need to send to internal servers, and another (probably the default?) that starts iteration after all of the internal items, which should just be a different pointer. At this point, there is no need to inspect each header by name, as that was effectively done at compile time when you put the protected headers at the front of the list.

Is this somewhat special? I mean, sure. But it wasn't long ago that a hash table was already in the special territory of data structures.

Edit: I should add that I'm not certain this idea would be better. Just more ideas on what you could do.

There’s a third party crate for this. C++’s STL also doesn’t have it by default.

The creation-order-preserving hash map is basically two data structures in one, it’s more complex and slower than a normal hash map, and IMO it’s rather bizarre and I have never really understood why anyone wants one.

I would be surprised if it was dramatically slower, all told. Though, fair that I have not benchmarked in a long time, here.

My main "idea" here is to stop from having to check all of the headers on a "per header" basis. Yes, you can make each check faster, as the TRIE does. You can also remove the entire reason to check individual headers by starting a traversal after where the internal headers are.

You could also go with something like making sure the first header is "InternalHeaderCount: N" where you then keep the internal headers segregated form the others by a simple count. (This assumes you have solid control over what is adding the headers internally, of course.)

(I also forgot to give kudos on the blog title. Any Die Hard reference is a good reference. :D )

It's especially unfortunate that the intuitive name, `std::map`, is that ordered and generally least useful option of the standard library's three hash map containers.

My last job did rely on ordered-ness of `QMap`, because the elements are listed in a Qt GUI and it could confuse users if those widgets randomly rearranged themselves. That's the only use-case I've personally encountered for an ordered hash map.