Question

Clojure with-local-vars和with-bindings的文档不足以让我区分这两者。任何提示？

Answer 1

var临时创建新的with-local-vars。现有var暂时被with-bindings反弹。在这两种情况下，绑定都是线程本地的。

请注意，就我所知，with-bindings主要用作帮助器，通过使用get-thread-bindings返回的映射来传递来自另一个上下文的绑定。不导入绑定时，类似的函数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，而不是符号 。它将给定的var / values映射推送到线程本地绑定的堆栈上并注意返回给定函数后删除它。这是一个低级别的功能。

（with-local-vars）允许您以命令式样式（变异状态）进行编码。

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

2 个答案: