On Fri, Sep 4, 2015 at 11:30 AM, Gregg Reynolds <[email protected]> wrote:
> I have a deftype that supports with-meta, but I can't figure out how to
> support caret reader syntax.
>
> To support with-meta, I include a "meta" field and implement IObj methods
> "meta" and "withMeta". Seems to work just fine:
>
> (with-meta (entity-map [:A/B] {:a 1}) {:foo "metadata here"})
>
> But this doesn't work: ^{:foo "metadata there"}(entity-map [:A/B] {:a 1})
>
Ok, so (entity-map...) is passed to the MetaReader as a PersistentList. Of
course. And if I say (def em (entity-map [:A/B] {:a 2})) and then say (def
em2 ^{:foo "bar"} em), then em gets passed as a symbol so the metadata does
not stick.
So it looks like you can only use caret metadata syntax with forms, rather
than types/values. If I wanted my deftype to support caret metadata, I
would have to defined a custom reader syntax for it, which as I understand
is not currently possible. Does that sound accurate?
Then again, the doc says
*Metadata (^)
Metadata is a map associated with some kinds of objects: Symbols, Lists,
Vector, Sets, Maps, tagged literals returning an IMeta, and record, type,
and constructor calls."
So let's try a Symbol:
(symbol? 'a) is true,
(instance? clojure.lang.IMeta 'a) is true, but
(meta ^{:foo 3} 'a) is nil, while
(meta ^{:foo 4} [1 2]) is {:foo 4}
So now I'm confused. Is the documentation just out of sync or am I
misunderstanding something?
Thanks,
Gregg
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