58 lines
2.5 KiB
Markdown
58 lines
2.5 KiB
Markdown
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---
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title: Clojure Create Local Variables with Let
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localeTitle: Clojure用Let创建局部变量
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---
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`let`是Clojure的基本组成部分。 `def`创建一个全局变量，而`let`创建一个局部变量。
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```
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(def x 5)
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(println x)
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; => 5
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; nil
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(let [x 2]
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(println x))
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; => 2
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; nil
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(println x)
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; => 5
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; nil
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```
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 [IDEOne吧！](https://ideone.com/xcNth2)
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此示例中的`x`实际上从未实际更改过。 `x`只是指我们的`let`绑定内部不同的东西。这可以是避免函数内部重复的有用方法。
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这非常有用。拥有太多全局变量可能会导致令人讨厌的错误和意外行为。
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```
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(def x 5)
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(defn add-5 [y] (+ xy))
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(add-5 5)
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; => 10
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(defn change-x []
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(def x 6))
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(change-x)
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; => nil
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(add-5 5)
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; => 11
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```
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 [IDEOne吧！](https://ideone.com/MFjA3C)
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哦哦！那不再是5了！当然，这个例子有点傻，但是使用太多的全局变量会导致像这个一样可怕的错误。
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**注意：**我们并不是真的在这里_重新分配_ `x` ，就像你在C语言中那样。我们只是创建一个恰好称为x的新变量。这是一个_非常**非常**_糟糕的主意。
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## 多个绑定
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`let`也可以一次定义多个变量，并可以为表达式赋值。
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```
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(let [spam "foo"
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ham (str "b" "ar")] ; str is a function that concatenates strings
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(println spam ham)) ; or converts variables into strings.
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; => foo bar
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; nil
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```
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 [IDEOne吧！](https://ideone.com/y5EBIM)
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| [上一页](//forum.freecodecamp.com/t/clojure-conditionals/18412) | [家](//forum.freecodecamp.com/t/clojure-resources/18422) | [下一个](//forum.freecodecamp.com/t/clojure-loop-recur/18418) |
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| [条件](//forum.freecodecamp.com/t/clojure-conditionals/18412) | [目录](//forum.freecodecamp.com/t/clojure-resources/18422) | [循环和重复](//forum.freecodecamp.com/t/clojure-loop-recur/18418) |
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