如何选择在Ruby中动态包含哪个版本的模块？ [英] How can I choose which version of a module to include dynamically in Ruby?

问题描述

我正在编写一个小型Ruby命令行应用程序，它使用标准库中的 fileutils 进行文件操作。根据用户调用应用程序的方式，我希望包含 FileUtils ， FileUtils :: DryRun 或 FileUtils :: Verbose 。

I'm writing a small Ruby command-line application that uses fileutils from the standard library for file operations. Depending on how the user invokes the application, I will want to include either FileUtils, FileUtils::DryRun or FileUtils::Verbose.

由于 include 是私有的， ，我不能把逻辑选择到对象的 initialize 方法中。 （这是我的第一个想法，从那以后我可以将有关用户选择的信息作为参数传递给 new 。）我想出了两个看似似乎的选项工作，但我不满意：

Since include is private, though, I can't put the logic to choose into the object's initialize method. (That was my first thought, since then I could just pass the information about the user's choice as a parameter to new.) I've come up with two options that seem to work, but I'm not happy with either:

1. 根据用户的选择在应用程序的命名空间中设置一个全局变量，然后在课堂上做一个条件包括：

1. Set a global variable in the app's namespace based on the user's choice, and then do a conditional include in the class:

class Worker
  case App::OPTION
  when "dry-run"
    include FileUtils::DryRun
    etc.

创建子类，唯一的区别是它们包含哪个版本的 FileUtils 。根据用户的选择选择合适的一个。

Create sub-classes, where the only difference is which version of FileUtils they include. Choose the appropriate one, depending on the user's choice.

class Worker
  include FileUtils
  # shared Worker methods go here
end
class Worker::DryRun < Worker
  include FileUtils::DryRun
end
class Worker::Verbose < Worker
  include FileUtils::Verbose
end

第一种方法似乎是DRY-er，但我希望有一些我没有想过的更直接的东西。

The first method seems DRY-er, but I'm hoping that there's something more straightforward that I haven't thought of.

推荐答案

那么如果它是私有的呢？

So what if it's private?

class Worker
  def initialize(verbose=false)
    if verbose
      (class <<self; include FileUtils::Verbose; end)
    else
      (class <<self; include FileUtils; end)
    end
    touch "test"
  end
end

这包括 FileUtils :: something 特别是 Worker 的元类 - 不在主工作者中 class。不同的工作人员可以这种方式使用不同的 FileUtils 。

This includes FileUtils::something in particular's Worker's metaclass - not in the main Worker class. Different workers can use different FileUtils this way.

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