As José said you’ll find the reasons there, I described the story in the release blog post - it started with a proposal on elixir-core.
Mainly concerns were about how often it’d be useful, that the right implementation would probably be protocols and that it’d be a bit overkill to add a protocol to the language for a feature with questioned general utilization.

It might be my interpretation, but there seems to be a chance that something like deep_merge will be added to Elixir at some time in the future if it turns out to be more useful/popular/something:

I believe though there are still too many questions to be answered before moving forward.

and

(…) as long as you pick a sane namespace, like DeepMerge, it should be fine. It is unlikely we would add it to Elixir as DeepMerge.

All that said, I think a library is a perfectly fine place for this to live, thanks to hex it’s easy to add and use and I hope the library lives up to all your quality standards and if not please tell me

Plus, I have to commend the elixir team for rejecting features. Imo it’s a hard but very necessary thing to do to keep a project lean and maintainable

Resurrection time

I just released 1.0.0 as the API has been proven stable, added some small goodies to go with it.

I consider it feature completely, so save good feature ideas, bugs, performance improvements, compiler warnings it shouldn’t see any more updates.

Enjoy deep merging

See https://github.com/elixir-lang/elixir/pull/5339 for a discussion on why it is not part of core.

I think so, yes.

• override behaviour (aka take the right side), at least for deep_merge as I could have a map with keywords as values but I don’t want them to be merged but rather treat them as values
• domain logic - not something I’ve actively tried but I think if you think about ecto’s queries and their keywords you could come up with a number of valid ways to “merge” them (intersection, union, append, connect with OR/AND), although I don’t think it’s a good thing to ever do
• given that duplicated keys are absolutely fine in keyword lists one might just wish to append - this is also true for merging “normal” lists (someone on the mailing list actually wanted this) - but it’s hard to distinguish as “normal” lists back keyword lists

I’m sure other people can and will come up with more ways

Totally agree.

Nice work guys, if the choice was mine, this language would not be as wonderful as it is! Awesome community and awesome maintainers!