什么时候在Ruby中使用Struct而不是Hash？ [英] When to use Struct instead of Hash in Ruby?

问题描述

我没有太多编程经验。但是，对我来说，Struct看起来有点类似于Hash。

• Struct可以做什么？


• 有什么结构可以做，哈希不能做什么？

在谷歌搜索后，结构的概念在C中很重要，但是我对C的了解不多。

解决方案

结构不同于以下方式使用hashmaps（除了代码的外观）：

• 一个结构具有一组固定的属性，而您将新的键添加到散列。


• 调用结构实例中不存在的属性将导致NoMethodError，而从哈希中获取不存在的键的值将返回nil。


• 即使结构具有相同的属性并且实例具有相同的值（即 Struct.new（：x）.new（42）== Struct.new（）），两个不同结构的实例永远不会相等。 ：x）.new（42）为false，而 Foo = Struct.new（：x）; Foo.new（42）== Foo.new（42）为真）。


• to_a 方法返回一个值的数组，而散列上的 to_a 则得到一个键值对的数组（其中pair表示二元数组 ）


• 如果 Foo = Struct.new（：x，：y，：z）您可以做 Foo.new（1,2,3）创建一个 Foo 的实例，而不必拼出属性名称。



$ b

所以要回答这个问题：当你想用一组已知属性建模对象时，使用结构体。当你想要建模任意使用hashmaps时（例如，计算每个单词出现在字符串中的频率或将昵称映射到全名等等）肯定不是结构的工作，而建模一个名字，年龄和地址的人会是一个完美的适合 Person = Struct.new（名字，年龄，地址））。



C结构与ruby结构几乎没有任何关系，所以不要让自己被这个混淆。




I don't have much programming experience. But, to me, Struct seems somewhat similar to Hash.

• What can Struct do well?
• Is there anything Struct can do, that Hash cannot do?

After googling, the concept of Struct is important in C, but I don't know much about C.

解决方案

Structs differ from using hashmaps in the following ways (in addition to how the code looks):

• A struct has a fixed set of attributes, while you add new keys to a hash.
• Calling an attribute that does not exist on an instance of a struct will cause a NoMethodError, while getting the value for a non-existing key from a hash will just return nil.
• Two instances of different structs will never be equal even if the structs have the same attributes and the instances have the same values (i.e. Struct.new(:x).new(42) == Struct.new(:x).new(42) is false, whereas Foo = Struct.new(:x); Foo.new(42)==Foo.new(42) is true).
• The to_a method for structs returns an array of values, while to_a on a hash gets you an array of key-value-pairs (where "pair" means "two-element array")
• If Foo = Struct.new(:x, :y, :z) you can do Foo.new(1,2,3) to create an instance of Foo without having to spell out the attribute names.

So to answer the question: When you want to model objects with a known set of attributes, use structs. When you want to model arbitrary use hashmaps (e.g. counting how often each word occurs in a string or mapping nicknames to full names etc. are definitely not jobs for a struct, while modeling a person with a name, an age and an address would be a perfect fit for Person = Struct.new(name, age, address)).

As a sidenote: C structs have little to nothing to do with ruby structs, so don't let yourself get confused by that.

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