Clojure with-local-vars没有创建线程本地绑定吗？

Question

在with-local-var文档中

varbinding=> symbol init-expr

Executes the exprs in a context in which the symbols are bound to
vars with per-thread bindings to the init-exprs. The symbols refer
to the var objects themselves, and must be accessed with var-get and
var-set

但是为什么thread-local?返回false呢？

user=> (with-local-vars [x 1] (thread-bound? #'x))
false

Answer 1

因为在您的示例中，x是到包含var的变量的本地绑定。#'x是(var x)的缩写，它会将x解析为当前名称空间中的全局变量。因为with-local-vars不影响全局x，所以thread-bound?返回false。

您需要使用x (而不是(var x))来引用with-local-vars创建的var。例如：

(def x 1)

(with-local-vars [x 2]
  (println (thread-bound? #'x))
  (println (thread-bound? x)))

输出：

false
true

还要注意，with-local-vars不会动态地重新绑定x。x仅在词法上绑定到with-local-vars块中的新var。如果调用引用x的函数，它将引用全局x。

如果您想要动态重新绑定x，则需要使用binding并将x动态化：

(def ^:dynamic x 1)

(defn print-x []
  (println x))

(with-local-vars [x 2]
  (print-x)) ;; This will print 1

(binding [x 2]
  (print-x)) ;; This will print 2