Comment made by: alexmiller
We must consider vectors or associative data structures other than maps. I also would prefer not to have a flag and to instead leave it open for variadic to remove multiple.
With an equivalent like:
(update-in [{:foo 1}] [0] dissoc :foo)
we would be left with {{[{}]}} so the existing way to do this does leave empty collections.
I also looked at some of the existing dissoc-in implementations that already exist - core.incubator, taoensso.encore, clj-http, medley, useful, plumbing, etc. Most work with a single key-path and leave empty collections - these seem largely to derive from the incubator version. The encore one works with multiple paths by separating the key path from the final leaf keys to dissoc (variadic). The medley, useful, and plumbing ones are map-only and remove empty maps.
I can't imagine that we would make a map-specific version of this in core (since all the other -in functions are generic) and thus I conclude that we would need a dissoc-in that left empty collections. Given that, I'm not sure whether dissoc-in provides enough value over update-in + dissoc to be worth adding to core at this point, especially since it exists in a variety of utility libraries (in many cases with differing semantics). We are then potentially breaking (or at least inconveniencing) many users of existing dissoc-in impls. I'm going to leave this open for comments, but I'm of a mind to decline this enhancement at this point.
