问题
In Clojure to address concurrency issues we can use an atom to write:
user=> (def my-atom (atom 0))
#'user/my-atom
user=> @my-atom
0
user=> (swap! my-atom inc)
1
user=> @my-atom
1
user=> (swap! my-atom (fn [n] (* (+ n n) 2)))
4
We know that this (in the Clojure implementation) is a wrapper around the Java Atomic object.
Interestingly enough, Atoms are replicated in ClojureScript, at a Syntactic level - even though JavaScript runtimes don't have an Atomic reference.
My question is, How are Atoms implemented in Clojurescript? Are they just an object Wrapper?
回答1:
It just returns and assigns the value.
In the source https://github.com/clojure/clojurescript/blob/master/src/main/cljs/cljs/core.cljs#L4081
(deftype Atom [state meta validator watches]
...
IDeref
(-deref [_] state)
...)
and https://github.com/clojure/clojurescript/blob/master/src/main/cljs/cljs/core.cljs#L4110
(defn atom
"Creates and returns an Atom ..."
([x] (Atom. x nil nil nil))
([x & {:keys [meta validator]}] (Atom. x meta validator nil)))
check the implementation of swap! and reset! you will find out:
(set! (.-state a) new-value)
then , go to https://github.com/clojure/clojurescript/blob/3bb97961cbc958aeaeac506222dc7b9dcb0e9fc1/src/clj/cljs/compiler.clj#L771 the set!, you will find the compiler just emits an 'assignment statement':
(defmethod emit* :set!
[{:keys [target val env]}]
(emit-wrap env (emits target " = " val)))
来源：https://stackoverflow.com/questions/21826514/how-are-atoms-implemented-in-clojurescript