On May 24, 1:01 am, Feng <hou...@gmail.com> wrote:
> Hi,
>
> clojure.contrib.types/deftype assumes data to tag are created fresh
> with no meta data. Would it be useful to have it update meta data if
> data are already initialized with meta data, e.g. from file or db with
> other meta data, but :type ::constructor are too program specific to
> be stored in there?
>
> A usage like following. x is read from database.
>
> user=> (meta x)
> {:last-updated #<Date Sun May 24 00:42:19 EDT 2009>}
> user=> (deftype ::person person)
> #<MultiFn clojure.lang.mult...@d063fd>
> user=> (meta (person x))
> {:type :user/person, :clojure.contrib.types/constructor user/
> person, :last-updated #<Date Sun May 24 00:42:19 EDT 2009>}
>
> Here is a simple patch. It merges deftype meta into original meta
> data, and it overrides existing deftype meta if they already exist
> (this is just to keep things simple. I haven't thought it much. Just
> assuming user knows new type should be compatible with old type in
> some context).
>
> Index: src/clojure/contrib/types.clj
> ===================================================================
> --- src/clojure/contrib/types.clj (revision 840)
> +++ src/clojure/contrib/types.clj (working copy)
> @@ -80,9 +80,9 @@
> ::constructor
> (quote ~(qualified-symbol constructor-
> name))}]
> (def ~constructor-name
> - (comp (fn [~'x] (with-meta ~'x meta-map#))
> ~constructor))
> + (comp (fn [~'x] (with-meta ~'x (merge (meta ~'x) meta-
> map#))) ~constructor))
> (defmethod deconstruct ~type-tag [~'x]
> - (~deconstructor (with-meta ~'x {})))))))
> + (~deconstructor (with-meta ~'x (dissoc (meta ~'x)
> {:type ::constructor}))))))))
sorry, should be
:type ::constructor
>
> (defmacro deftype-
> "Same as deftype but the constructor is private."
>
> Regards,
> - Feng
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