A possible bug involving maps & `extend-protocol`

[Josh Tilles]

I would expect the following code to typecheck, but I'm stumped on some errors. Am I missing something? Or should I create a bug report on JIRA?

Code:

 (ns demo

   (:require [clojure.core.typed :as t]))

(t/defprotocol Connectable

  (add-connection [db, connection :- java.sql.Connection]

    :- (t/HMap :mandatory {:connection java.sql.Connection}

               :optional {:connection-string String

                          :level t/AnyInteger

                          :legacy Boolean}))

  (get-level [db]

    :- t/AnyInteger))

(extend-protocol Connectable

  String

  (add-connection [s connection] {:connection connection :level 0 :connection-string s})

  (get-level [_] 0)

  clojure.lang.Associative

  (add-connection [m connection] (assoc m :connection connection))

  (get-level [m] (or (:level m) 0))

  nil

  (add-connection [_ connection] {:connection connection :level 0 :legacy true})

  (get-level [_] 0))

Output of (t/check-ns 'demo):

Type Error (demo.clj:19:34) Cannot assoc args `[(t/Val :connection) {:then tt, :else ff}] [java.sql.Connection {:then tt, :else ff} {:id connection__#0}]` on (Associative t/Any t/Any)

in: (assoc m :connection connection)

Type Error (demo.clj:20:18) Type mismatch:

Expected: t/AnyInteger

Actual: t/Any

in: or__4238__auto__

ExceptionInfo Type Checker: Found 2 errors  clojure.core/ex-info (core.clj:4593)

[Ambrose Bonnaire-Sergeant]

I would use t/pred to cast the Associative argument to the expected HMap type

before assoc'ing it.

eg. {:pre [((t/pred (HMap ..)) m)]}

There's a possible enhancement where you might be able to specify the static type

you're expecting for a particular extend-type dispatch, but I haven't thought it through.

Thanks,

Ambrose

[Josh Tilles]

Thanks a bunch Ambrose! That did the trick. (Plus, I now know about clojure.core.typed/pred!)

By the way, is it appropriate to be bringing these sorts of questions to the mailing list? Like, should I instead start with IRC or JIRA?

[Ambrose Bonnaire-Sergeant]

This is the preferred place.