In the let case, the *pool* will be tagged with the proper type so the
ambiguity is detected.
In the def case, the *pool* will be seen as an object and the compiler is
just deferring to reflection at runtime to figure it out. If you turn on
*warn-on-reflection*, you'll see a reflection warning in this case.
Reflection is just picking the first one that matches in that case. If you
type hinted the def case, you'd see the same error.
On Saturday, July 16, 2011 6:13:11 AM UTC-5, Alf wrote:
>
> Hi guys. Experimenting a bit with code from "The joy of Clojure", and
> I ran into a little problem. Trying to run this in the REPL gives the
> following error:
>
> user=> (import [java.util.concurrent Executors])
> java.util.concurrent.Executors
>
> user=> (let [*pool* (Executors/newFixedThreadPool (+ 2
> (.availableProcessors (Runtime/getRuntime))))]
> (defn dothreads! [f & {thread-count :threads
> exec-count :times
> :or {thread-count 1 exec-count 1}}]
> (dotimes [t thread-count]
> (.submit *pool* #(dotimes [_ exec-count] (f))))))
> java.lang.IllegalArgumentException: More than one matching method
> found: submit (NO_SOURCE_FILE:7)
>
>
> However if I define pool as a Var it seems to work fine:
>
> user=> (import '(java.util.concurrent Executors))
> java.util.concurrent.Executors
>
> user=> (def *pool* (Executors/newFixedThreadPool
> (+ 2 (.availableProcessors (Runtime/getRuntime)))))
> #'user/*pool*
>
> user=> (defn dothreads! [f & {thread-count :threads
> exec-count :times
> :or {thread-count 1 exec-count 1}}]
> (dotimes [t thread-count]
> (.submit *pool* #(dotimes [_ exec-count] (f)))))
> #'user/dothreads!
>
> (from
> https://github.com/joyofclojure/book-source/blob/master/src/joy/mutation.clj
> )
>
> ExecutorService has three submit methods, and two with one parameter,
> a Runnable and a Callable. Since Clojure functions are both, I
> understand the compiler error, but why does it work when *pool* is a
> Var?
>
> The "let" version works when I cast the function to Runnable or
> Callable, just wondering why there is a difference.
>
> Cheers,
> Alf
>
>
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