Clojure让绑定表单 [英] Clojure let binding forms

问题描述

我想了解如何让绑定在关闭地图工作。从我的理解let后面跟一个向量，其中第一个项目是我想要绑定的符号，后面是我想要绑定的值。

I'm trying to understand how let bindings work in closure in regards to maps. From my understanding let is followed by a vector where the first item is the symbol I want bound, followed by the value I want to bind it to. So

(let [a 1 b 2] a) 

会给出值1。

所以如果我声明映射如

(def people {:firstName "John" :lastName "Doe"})

而我想绑定键firstName，这将是一个简单的Hello Person的正确形式

And I want to bind the key firstName then this would be the correct form for a simple "Hello Person"

(let [personName (:firstName people)] (str "hello " personName))

b $ b

这在Clojure的网站上有效，但是在 http://clojure.org/special_forms#binding

This works, however on the Clojure website http://clojure.org/special_forms#binding-forms they show a different form which also works

(let [{personName :firstName} people] (str "hello " personName))

这两个代码段都可以正常工作， m混淆了第二个语法。这只是语法糖还是重复的工作方式，是比另一个更惯用的吗？

Both code snippets work and I understand why the first version works but I'm confused on the syntax on the second. Is this just syntactical sugar or a duplicate way of working and is one more idiomatic than the other?

推荐答案

最后一种形式是地图绑定解构。如果你想将多个变量绑定到同一个地图的不同元素，这是最有用的：

The last form is Map binding destructuring. It's most useful if you want to bind multiple variables to different elements of the same map:

(let [{firstName :firstName lastName :lastName address :address} people]
    (str "hello " firstName " " lastName ", I see you live at " address))

如果你使用以前的语法写出来，它将是：

If you were to write this out using the previous syntax, it would be:

(let [firstName (:firstName people) lastName (:lastName people) address (:address people)]
    (str "hello " firstName " " lastName ", I see you live at " address))

如您所见，这可以避免您重复人在每个绑定。如果地图是计算的结果，它避免了必须绑定一个变量，所以你可以重复它。

As you see, this saves you from having to repeat people in each binding. And if the map is the result of a computation, it avoids having to bind a variable to that so you can repeat it.

解构也允许你布局绑定构造的格式与您访问的数据结构类似。这使得它对于复杂的结构更加惯用。

Destructuring also allows you to lay out the binding construct in a format that's similar to the data structure you're accessing. This makes it more idiomatic for complex structures.

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