Attaching type hints to a Clojure delayed call -


i'm attempting put handles on java objects aren't available @ compile time, available @ runtime, in vars follows:

(def component-manager (delay (somejavaobject/gethandle)))

(if better mechanism delays available, welcome).

when these objects used, reflection warning generated. these frequent, i've tried avoid following:

(def my-handle ^somejavaobject (delay (somejavaobject/gethandle)))

unfortunately, reflection warning still generated in case.

modifying references works:

(.foo ^somejavaobject @my-handle)

...but uglifies code substantially.

wrapping in macro adds type hints seems obvious approach:

(def my-handle' (delay (somejavaobject/gethandle))) (defmacro my-handle []   (with-meta '(deref my-handle')              {:tag somejavaobject}))

...and looks should right thing:

=> (set! *print-meta* true) => (macroexpand '(my-handle)) ^somejavaobject (deref my-handle')

...but doesn't hold true when rubber hits road:

=> (.foo (my-handle)) reflection warning, no_source_path:1 - reference field foo can't resolved.

what's right way this?

i'd offer 2 different solutions:

1. delay

first off, wanted post answer shows how problem can recreated. (as worded, question abstract , cannot run in repl.)

(set! *warn-on-reflection* true) (def rt (delay (runtime/getruntime))) (.availableprocessors @rt) ; reflection warning

you mention don't following approach because consider verbose:

(.availableprocessors ^java.lang.runtime @rt) ; no warning

i tried following, did not solve reflection warning:

(def rt (delay ^java.lang.runtime (runtime/getruntime))) (.availableprocessors @rt) ; reflection warning

conclusion: if want use delay, ankur's answer works great. adapt example:

(def delayed-runtime (delay (runtime/getruntime))) (defn ^java.lang.runtime get-runtime [] @delayed-runtime) (.availableprocessors (get-runtime)) ; no warning

2. memoize

you might consider using memoization, requires less code:

(def ^java.lang.runtime get-runtime (memoize #(runtime/getruntime))) (.availableprocessors (get-runtime)) ; no warning

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