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[CLJ-1378] Hints don't work with #() form of function Created: 11/Mar/14  Updated: 10/Jun/14

Status: Open
Project: Clojure
Component/s: None
Affects Version/s: None
Fix Version/s: Release 1.7

Type: Enhancement Priority: Major
Reporter: Roy Varghese Assignee: Unassigned
Resolution: Unresolved Votes: 1
Labels: interop, typehints

Attachments: File clj-1378.diff     File clj-1378-v2.diff    
Patch: Code
Approval: Vetted

 Description   
;; WORKS
(deftest test-add-job
  (let [pool (java.util.concurrent.Executors/newFixedThreadPool 10)
        counter 50000
        f (fn [])]
    (dotimes [i counter]
      (.submit pool ^Runnable  f ))
    (Thread/sleep 1000)
    (is (= counter (count (all-jobs))))))

;; FAILS
(deftest test-add-job
  (let [pool (java.util.concurrent.Executors/newFixedThreadPool 10)
        counter 50000]
    (dotimes [i counter]
      (.submit pool ^Runnable  #()))
    (Thread/sleep 1000)
    (is (= counter (count (all-jobs))))))

Caused by: java.lang.IllegalArgumentException: More than one matching method found: submit
	at clojure.lang.Compiler.getMatchingParams(Compiler.java:2380)
	at clojure.lang.Compiler$InstanceMethodExpr.<init>(Compiler.java:1412)
	at clojure.lang.Compiler$HostExpr$Parser.parse(Compiler.java:952)
	at clojure.lang.Compiler.analyzeSeq(Compiler.java:6560)
	... 87 more


 Comments   
Comment by Jozef Wagner [ 12/Mar/14 4:03 AM ]

Functions do have metadata, but Compiler does not look in them for type hints.

user=> (with-meta #() {:foo :bar})
#<clojure.lang.AFunction$1@779325ee>

When compiler is determining which native method to use, it matches method signature with classes of given args. There is a getJavaClass() method in Compiler.java which returns a class for given expression. Vars expressions and local bindings use :tag metadata to override this class, but most other expressions don't. Compiler parses #() into a FnExpr, which always return AFunction as its class.

Most of time this approach is OK, as AFunction implements Runnable and Callable so there is no need for type hint. However, in this particular case, there are overrides for both Runnable and Callable, and as AFunction can be either of them, the expression is ambiguous.

Comment by Jozef Wagner [ 12/Mar/14 4:17 AM ]

Patch added, following expression will now run without error

(.submit (java.util.concurrent.Executors/newCachedThreadPool) ^Runnable #())
Comment by Alex Miller [ 12/Mar/14 9:34 AM ]

Could you add a test to the patch?

Comment by Jozef Wagner [ 12/Mar/14 2:53 PM ]

Attached patch clj-1378-v2.diff which contains both fix and test.

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