clojure - Clojure 中 with-local-vars 和 with-bindings 之间的区别

Question

Clojure 的文档with-local-vars并with-bindings不足以让我区分两者。有什么提示吗？

Answer 1

Newvar是由 临时创建的with-local-vars。现有vars 暂时反弹with-bindings。在这两种情况下，绑定都是线程本地的。

请注意，with-bindings据我所知，它主要用作帮助器，通过使用返回的映射从另一个上下文传递绑定get-thread-bindings。当不导入绑定时，类似的功能binding会更典型。

说明性示例：

(binding [*out* (new java.io.StringWriter)] 
  (print "world!") (str "hello, " *out*))
;=> "hello, world!"

(with-local-vars [*out* (new java.io.StringWriter)] 
  (print "world!") (str "hello," *out*))
;=> world!"hello,#<Var: --unnamed-->"

(with-local-vars [foo (new java.io.StringWriter)] 
  (.write @foo "world") (str "hello, " @foo))
;=> "hello, world"

(binding [foo (new java.io.StringWriter)] 
  (.write @foo "world") (str "hello, " @foo))
;=> CompilerException java.lang.RuntimeException: 
;     Unable to resolve var: foo in this context...

Answer 2

(with-bindings) 期望绑定映射的键是 Vars，而不是 symbols。它将给定的 var/values 映射推送到线程本地绑定的堆栈上，并在给定函数返回后注意将其删除。这是一个低级功能。

(with-local-vars) 允许您以命令式风格（变异状态）进行编码。