On Tue, Dec 15, 2009 at 1:11 PM, Richard Newman <holyg...@gmail.com> wrote:
>> Isn't the whole point of a struct that it guarantees that certain keys
>> are present?
>
> Oh, I agree -- dissoc on a struct-map would return a non-struct-map.
> I'm not suggesting that struct-maps should be able to be dissociated
> from one of their keys, I'm wondering whether it's better to return an
> array-map or hash-map from dissoc rather than blow up.
>
> (Or whether there should be a `without-keys` function that behaves
> much like dissoc but works on any map, and have rename-keys and other
> "implicit dissoc" functions use that instead. rename-keys on a struct-
> map's core keys implies an abandonment of struct-ness, no?)
>
> I suppose the question is "are struct-maps 'structs' or
> maps?" (speaking ontologically). If they're structs, then it's happy
> coincidence that the map get/assoc functions work on them, and
> slightly confusing that they print as ordinary maps. If they're maps,
> where their struct-ness is an optimization, then dissoc should work in
> the same way that assoc on an array-map can sometimes return a hash-map.
>
> The main reason I bring this up is that I had no reason to suspect
> that the maps returned from my SQL queries were actually struct-maps.
> They printed like any other map, and work correctly for every non-
> removing map operation. Having some subset of maps error on core API
> operations seems opposed to abstraction-oriented programming. It trips
> my disgust switch to see code like
>
> (rename-keys
> (if (struct-map? m)
> (into {} m)
> m)
> {:foo :bar})
>
Yes. The behavior for the new deftypes, when used as maps, is as you
desire - a dissoc of a field key yields an ordinary map (no longer of
the deftype type).
Enhancements to structs are on hold pending analysis of their utility
in light of deftypes.
Rich
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