如何更改 Struct 属性的默认值? [英] How to change the default value of a Struct attribute?

问题描述

根据文档Struct 的未设置属性设置为 nil:

According to the documentation unset attributes of Struct are set to nil:

未设置参数默认为零.

是否可以为特定属性指定默认值?

Is it possible to specify the default value for particular attributes?

例如对于下面的Struct

For example, for the following Struct

Struct.new("Person", :name, :happy)

我希望属性 happy 默认为 true 而不是 nil.我怎样才能做到这一点?如果我做如下

I would like the attribute happy to default to true rather than nil. How can I do this? If I do as follows

Struct.new("Person", :name, :happy = true)

我明白

-:1: syntax error, unexpected '=', expecting ')'
Struct.new("Person", :name, :happy = true)
                                    ^
-:1: warning: possibly useless use of true in void context

推荐答案

这也可以通过将 Struct 创建为子类并覆盖初始化 使用默认值，如下例所示:

This can also be accomplished by creating your Struct as a subclass, and overriding initialize with default values as in the following example:

class Person < Struct.new(:name, :happy)
    def initialize(name, happy=true); super end
end

一方面，这种方法确实会导致一些样板；另一方面，它可以很好且简洁地完成您想要的操作.

On one hand, this method does lead to a little bit of boilerplate; on the other, it does what you're looking for nice and succinctly.

一个副作用(根据您的偏好/用例，可能是好处也可能是烦恼)是您失去了所有属性的默认 Struct 行为，默认为 nil -- 除非您明确将它们设置为如此.实际上，上述示例将使 name 成为必需参数，除非您将其声明为 name=nil

One side-effect (which may be either a benefit or an annoyance depending on your preferences/use case) is that you lose the default Struct behavior of all attributes defaulting to nil -- unless you explicitly set them to be so. In effect, the above example would make name a required parameter unless you declare it as name=nil

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