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[CLJ-1378] Hints don't work with #() form of function Created: 11/Mar/14  Updated: 29/Aug/14  Resolved: 29/Aug/14

Status: Closed
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: Completed Votes: 1
Labels: interop, typehints

Attachments: File clj-1378.diff     File clj-1378-v2.diff    
Patch: Code and Test
Approval: Ok

 Description   

Example showing how a local fn can be hinted but an anonymous function cannot:

;; OK
user> (let [ex (java.util.concurrent.Executors/newFixedThreadPool 1)
            f (fn [])]
        (.submit ex ^Runnable f))
nil
;; ERROR - this should work the same as the previous
user> (let [ex (java.util.concurrent.Executors/newFixedThreadPool 1)]
        (.submit ex #()))
CompilerException java.lang.IllegalArgumentException: More than one matching method found: submit, compiling:(/private/var/folders/7r/_1fj0f517rgcxwx79mn79mfc0000gn/T/form-init7901279404687292754.clj:3:9)

Cause: Functions have metadata, but Compiler does not look in them for type hints. Var expressions and local bindings use :tag metadata to override return of getJavaClass(). Compiler parses #() into a FnExpr, which always return AFunction as its class.

Proposed: Change FnExpr.getJavaClass() to return tag as type if it is available.

Patch: clj-1378-v2.diff

Screened by: Alex Miller



 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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