如何在AOT编译之前设置动态变量 [英] How to set a dynamic var before aot compile

问题描述

我想在给定的命名空间中有一个 * flag * 变量，该变量仅在:aot 编译时设置为 true .

I want to have a *flag* variable in a given namespace that is set to true only when :aot compiling.

有没有办法做到这一点?

Is there a way to do that?

推荐答案

您的问题有点复杂，因为Clojure自身的动态性质的定义，因此它与C的 #ifdef 几乎不存在等效性编译时发生的其他机制，但这是一种解决方法:

Your issue is kind of complicated because the definition of Clojure's own dynamic nature, so there's no rough equivalent of C's #ifdef or some other mechanism that happens at compile time, but here's a workaround:

我用 lein新应用程序flagdemo 创建了一个Leiningen项目.此技巧将使用动态var * compile-files * 来检测何时执行AOT(如上述@Biped Phill)，并将资源保存在已编译代码的类路径中:

I created a Leiningen project with lein new app flagdemo. This trick detects when AOT is performed, as @Biped Phill mentioned above, using the dynamic var *compile-files*, and saves a resource in the classpath of the compiled code:

代码如下:

(ns flagdemo.core
  (:gen-class))

(def flag-path "target/uberjar/classes/flag.edn")

(defn write-flag [val]
  (try (spit flag-path (str val)) (catch Exception _)))

(defn read-flag []
  (some-> (clojure.java.io/resource "flag.edn") slurp clojure.edn/read-string))

(write-flag false)

(when clojure.core/*compile-files*
  (write-flag true))

(defn -main
  [& args]
  (println "Flag is" (read-flag)))

因此，当使用 lein run 加载文件 时，或者将其加载到REPL中时，它将尝试写入值 false .

So, when the file loads using, say, lein run or when you load it in the REPL, it will try to write an EDN file with the value false.

使用 lein uberjar 编译软件包时，它将加载名称空间并发现已定义 * compile-files * ，因此它将保存打包的EDN文件以JAR作为资源.

When you compile the package using lein uberjar, it loads the namespace and finds that *compile-files* is defined, thus it saves an EDN file that is packaged with the JAR as a resource.

函数 read-flag 只是尝试从类路径中加载EDN文件.

The function read-flag just tries to load the EDN file from the classpath.

它是这样的:

$ lein clean
$ lein run
Flag is nil

$ lein uberjar
Compiling flagdemo.core
Created /tmp/flagdemo/target/uberjar/flagdemo-0.1.0-SNAPSHOT.jar
Created /tmp/flagdemo/target/uberjar/flagdemo-0.1.0-SNAPSHOT-standalone.jar

$ java -jar target/uberjar/flagdemo-0.1.0-SNAPSHOT-standalone.jar
Flag is true

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