Clojure

Using 'def with metadata {:type :anything} throws ClassCastException during printing

Details

  • Type: Defect Defect
  • Status: Open Open
  • Priority: Minor Minor
  • Resolution: Unresolved
  • Affects Version/s: Release 1.4
  • Fix Version/s: None
  • Component/s: None
  • Labels:
    None
  • Environment:
    Ubuntu, lein 1.7.1 - lein repl
  • Patch:
    Code and Test
  • Approval:
    Vetted

Description

Specific to setting :type meta on a var:

user=> (def ^{:type :anything} mydef 1)
#<main$repl clojure.main$repl@6193b845>
CompilerException java.lang.ClassNotFoundException: main.clj:257, compiling:(NO_SOURCE_PATH:13:20)
ClassCastException clojure.lang.Var cannot be cast to clojure.lang.IObj  clojure.core/with-meta (core.clj:214)
user=> (pst *e)
ClassCastException clojure.lang.Var cannot be cast to clojure.lang.IObj
	clojure.core/with-meta (core.clj:214)
	clojure.core/vary-meta (core.clj:640)
	clojure.core/fn--5420 (core_print.clj:76)
	clojure.lang.MultiFn.invoke (MultiFn.java:232)
	clojure.core/pr-on (core.clj:3392)
	clojure.core/pr (core.clj:3404)
	clojure.core/apply (core.clj:624)
	clojure.core/prn (core.clj:3437)
	clojure.main/repl/read-eval-print--6627 (main.clj:241)
	clojure.main/repl/fn--6636 (main.clj:258)
	clojure.main/repl (main.clj:258)
	clojure.main/repl-opt (main.clj:324)

If it is intended to forbid setting the :type metadata, then there should be an appropriate error message instead of the ClassCastException.

Cause: This is caused by the printer dispatch function

(defmulti print-method (fn [x writer]
                         (let [t (get (meta x) :type)]
                           (if (keyword? t) t (class x)))))

which ends up calling the default dispatch, which tries to vary-meta.

Solution:

Patch:

Screened by:

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Dates

  • Created:
    Updated: