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[CLJ-1162] Error Message when calling deref on a non-IDeref is unhelpful Created: 12/Feb/13  Updated: 03/Sep/13

Status: Open
Project: Clojure
Component/s: None
Affects Version/s: Release 1.5
Fix Version/s: None

Type: Enhancement Priority: Minor
Reporter: Julian Birch Assignee: Unassigned
Resolution: Unresolved Votes: 2
Labels: errormsgs

Found this on ubuntu, lein 2, Clojure 1.5 snapshot, but it's obvious from inspection

Attachments: Text File CLJ-1162-p1.patch    
Patch: Code


If you just type "@1" is the repl, on previous versions you'll get an error that Long cannot be cast to IDeref. In 1.5, the error message is that it cannot be cast to java.util.concurrent.Future. This is because it assumes that anything that isn't an IDeref is automatically a Future. The deref method should generate a custom error stating that the type you've passed in is neither an IDeref nor a Future.

Comment by Gary Fredericks [ 26/May/13 3:00 PM ]

Attached a patch that implements the old behavior (can't cast to IDeref), which strikes me as good enough considering the support for j.u.c.Future seems rather an edge case (being that clojure's futures are themselves IDeref).

The weirdest thing I did was to use clojure.core/cast to unconditionally throw a ClassCastException. Let me know if that's weird and I'll do something different.

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