“ #map（& proc）”如何进行？内省模块类时可以使用成语吗？

问题描述

我发现了一个接受答案。该代码显然可以在REPL中使用。例如：

I found an interesting but unexplained alternative to an accepted answer. The code clearly works in the REPL. For example:

module Foo
  class Bar
    def baz
    end
  end
end
Foo.constants.map(&Foo.method(:const_get)).grep(Class)
=> [Foo::Bar]

但是，我不完全理解此处使用的惯用语。特别是，我不理解& Foo 的使用，这似乎是某种封闭，或者#grep的特定调用如何对结果进行操作。

However, I don't fully understand the idiom in use here. In particular, I don't understand the use of &Foo, which seems to be some sort of closure, or how this specific invocation of #grep operates on the result.

到目前为止，我已经能够解析其中的点点滴滴，但是我没有真正看到它们如何组合在一起。这是我对示例代码的理解。

So far, I've been able to parse bits and pieces of this, but I'm not really seeing how it all fits together. Here's what I think I understand about the sample code.

1. Foo .constants 以符号形式返回模块常量数组。

1. Foo.constants returns an array of module constants as symbols.

method（：const_get）使用进行方法查找并返回闭包。

method(:const_get) uses Object#method to perform a method lookup and return a closure.

Foo.method（：const_get）.call：Bar 是一个闭包，它返回类中常量的限定路径。

Foo.method(:const_get).call :Bar is a closure that returns a qualified path to a constant within the class.

& Foo 似乎是。文档说：

我也不确定我是否完全理解在特定情况下的含义。为什么要进行？

I'm not sure I fully understand what that means in this specific context, either. Why a Proc? What "tricks," and why are they necessary here?

grep（Class）的作用是什么？ Foo.constants.map {| c | Foo.const_get（c）} 。 grep 使用 === 来选择元素，因此它将仅获取引用类的常量，而不获取其他值。可以通过在 Foo 中添加另一个常量来验证这一点，例如 Baz = 1 ，将不会得到 grep 。

So in the end this is just a pointfree way of saying Foo.constants.map { |c| Foo.const_get(c) }. grep uses === to select elements, so it would only get constants that refer to classes, not other values. This can be verified by adding another constant to Foo, e.g. Baz = 1, which will not get grepped.

如果您还有其他问题，请将其添加为评论，我会尽力澄清。

If you have further questions please add them as comments and I'll try to clarify them.

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