Re: surprising behaviour from dissoc on records
Interesting. I think it makes sense in that `dissoc` is a function for
removing a kv pair from a map, not a function for setting v to nil given a
k. I could definitely see tripping up on this though.
On Friday, February 19, 2016 at 8:07:16 AM UTC-8, Alex Miller wrote:
>
> 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
>>
>>
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
---
You received this message because you are subscribed to the Google Groups
"Clojure" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to clojure+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
Re: surprising behaviour from dissoc on records
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
>
>
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
---
You received this message because you are subscribed to the Google Groups
"Clojure" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to clojure+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
surprising behaviour from dissoc on records
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
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
---
You received this message because you are subscribed to the Google Groups
"Clojure" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to clojure+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
