You can find some of the background for this
at http://clojure.org/reference/datatypes. Records are intended to capture
"application domain information" - where the fields are known. Dissoc'ing
means you are removing not just a value, but the whole "field", and the
implication here is that you devolve from a thing of that "type" to a plain
map. Similarly, "empty" is not implemented on records (because you then
remove all the "fields").
This is an intentional choice made by Rich in the design of records. I
think it's reasonable to argue that this creates some surprises in the use
of records - particularly in dissoc and empty. Afaik there is no plan for
this behavior to change, however.
On Friday, February 19, 2016 at 8:30:47 AM UTC-6, Stig Brautaset wrote:
>
>
> Dissoc behaviour on records really surprised me:
>
> user> (defrecord Foo [bar])
> ;; => user.Foo
> user> (def foo (->Foo nil))
> ;; => #'user/foo
> user> (dissoc foo :bar)
> ;; => {}
> user> (assoc foo :bar nil)
> ;; => #user.Foo{:bar nil}
>
> It lead to a bug where a component of mine, which I was using to
> dispatch in a multimethod was replaced with an empty map:
>
>
> https://github.com/stig/accounts/commit/f4124b69cfc9fdc201b29f97e33a5b7bd6279e7f
>
>
> *toy project alert*
>
> As an aside, I'm now starting to understand why all the components
> examples use `assoc foo :bar nil` rather than dissoc...
>
> Stig
>
>
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