James,
I've been thinking about protocols. Yes, I can now put them on an
aggregate, but there may be a lot of places where it is better not to use a
protocol and just use functions instead.
The code below does not use a protocol and I rather like it. In other cases
we can use functions to achieve indirection by calling functions in an
aggregate. So it remains to be seen if there is a good case for using a
protocol with an aggregate. But at least I know how now--create an
aggregate in a record.
Bill
(ns aatree.closer-trait
(:require [clojure.tools.logging :as log]))
(set! *warn-on-reflection* true)
(defn on-close [this f]
(let [fsa (:closer-fsa this)]
(if fsa
(do
(swap! fsa
(fn [fs]
(if fs
(conj fs f)
(atom (list f)))))
this)
(assoc this :closer-fsa (atom (list f))))))
(defn- do-closer [this fs]
(when fs
(try
((first fs) this)
(catch Exception e
(log/warn e "exception on close")))
(recur this (next fs))))
(defn do-close [this]
(let [fsa (:closer-fsa this)]
(if fsa
(let [fs @fsa]
(if fs
(if (compare-and-set! fsa fs nil)
(do-closer this fs)
(recur this)))))))
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