Keep ordering of deserialized maps

[dlo9]

Serde's yaml deserialization supports maintaining the order of map types (at least in yaml/json, haven't looked at other formats) by using LinkedHashMap instead of HashMap. Quickly perusing through config-rs, it looks like the table value uses HashMap and so will always lose the ordering of a map.

AFAICT, a fix to this would be as simple as changing HashMap to LinkedHashMap in the appropriate places, but since that type is exposed to the API, it could be considered a breaking change. Would the project be receptive to such a change?

[matthiasbeyer]

Hi,

thanks, that's a nice idea to pursue. Maybe we can work together and explore whether it would be possible to make the YAML de/serialization mechanisms generic over HashMap vs LinkedHashMap? I don't know whether such a thing is possible, but maybe it is...
If not, maybe adding a new "backend type" which explicitely uses LinkedHashMap is possible?

If all fails, we can always release breaking changes as long as we're in version 0.x.y, although I would prefer to not have to do this.

Long story short: Consider me interested! 😆

[dlo9]

Great! I'll see if can can find some time in the next few days to make a test case and initial breaking implementation, and then we can go from there

[dlo9]

Just made a draft PR for an initial implementation -- there's a few things I discovered while making the change which I'd like to fix, but it will probably take me a few days to get around to. In the meantime, let me know if you have any changes or requested comments and I'll make it ready when I'm happy with the PR