blocks|key|2025016|text|当人们谈论嵌套方法/函数时，他们通常指的是仅在封闭方法中可见/可用的东西。但您的示例并非如此-一旦定义，任何人都可以在该对象上调用它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2025017|您展示的是ruby的单例方法:在类的一个实例上定义方法的能力(例如，当人们说ruby中的类方法时，这些方法实际上是Class类实例上的单例方法)。|offset|length|style|CODE|2025018|至于是否有更好的方法，这是无法回答的，因为你还没有说你试图解决的问题是什么。|2025019|entityMap^0|0|1L|5|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@$D|N|E|O|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|K|$]]

When people talk about nested methods/functions, they generally mean things that are only visible/usable from within the enclosing method. This isn't true of your example - once defined, it can be called on that object by anyone. 

What you're showing is Ruby's singleton methods: the ability to define a method on one instance of a class (for example when people say class method in ruby, those are actually singleton methods on that instance of the <code>Class</code> class)

As to whether there is a better way, that is unanswerable since you haven't said what the problem you are trying to solve is.

blocks|key|1927238|text|在方法中调用def通常是错误的方式。您需要的是定义一个封装此方法和其他方法的模块，然后根据需要将其混合到任何对象中：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1927239|module+DateExtensions
++def+is_friday?
++++wday+==+5
++end
end|code-block|syntax|javascript|1927240|值得注意的是，strftime可能会返回“星期五”以外的值，因为本地化可能会生效。根据你所在的位置，你可以得到"Freitag“或"Vendredi”。wday方法返回一个可预测的数值。|1927241|现在，您可以将以下代码混合在一起：|1927242|class+Test
++def+today
++++date+=+Date.today

++++date.extend(DateExtensions)

++++date
++end
end|1927243|通过在模块中声明这些方法，很明显它们是包的一部分。这也意味着你不需要为你创建的每个Date实例定义一个全新的方法。|1927244|一种更Ruby的方式是定义你自己的Date子类，它添加了这个额外的行为。|1927245|entityMap^0|6|3|0|0|7|8|24|4|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|15|8|@]|D|@]|E|$]]|$1|O|3|P|5|H|7|16|8|@]|D|@]|E|$I|J]]|$1|Q|3|R|5|6|7|17|8|@]|D|@]|E|$]]|$1|S|3|T|5|6|7|18|8|@]|D|@]|E|$]]|$1|U|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|V|$]]

Calling <code>def</code> inside a method is usually the wrong way to do this. What you want is to define a module that encapsulates this and potentially other methods, then mix that in on any objects as necessary:

<pre><code>module DateExtensions
 def is_friday?
 wday == 5
 end
end
</code></pre>

It's worth noting that <code>strftime</code> might return values other than "Friday" because localization may be in effect. You could get "Freitag" or "Vendredi" depending on where you are. The <code>wday</code> method returns a predictable numerical value.

Now you can mix this in:

<pre><code>class Test
 def today
 date = Date.today

 date.extend(DateExtensions)

 date
 end
end
</code></pre>

By declaring these methods inside a module it's a lot more obvious they're part of a package. It also means you don't need to define a brand new method for each instance of a Date you create.

A more Ruby way of doing this is to define your own subclass of Date that adds in this additional behaviour.

blocks|key|575430|text|方法定义是代码，就像其他代码一样。它们可以像任何其他代码一样出现在方法中。就像任何其他代码一样，它们将在每次方法运行时执行。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|575431|所以，这个|575432|class+Foo
++def+foo
++++def+bar
++++end
++end
end|code-block|syntax|javascript|575433|不是嵌套方法，而仅仅是定义方法的方法。很容易看出，这不是一个嵌套的方法，只需调用它两次，注意生成的警告并检查周围模块的已定义方法：|575434|foo+=+Foo.new

Foo.public_instance_methods(false)
#=>+[:foo]

foo.foo

Foo.public_instance_methods(false)
#=>+[:foo,+:bar]

foo.foo
#+(irb):3:+warning:+method+redefined;+discarding+old+bar
#+(irb):3:+warning:+previous+definition+of+bar+was+here|575435|正如您所看到的，bar并没有嵌套在foo中，而是在Foo类中的foo之外定义的。它只在foo运行后定义，并且每次foo运行时都会重新定义。|offset|length|style|CODE|575436|当然，您的示例有点不同，因为它不会一直覆盖同一个类中的方法，而是在每次调用时都在不同的类中定义它。|575437|请注意，有禁止这种使用的计划，请参阅Feature+#11665:+。|575438|575439|，但是你怎么称呼它呢？|blockquote|575440|575441|575442|它是一种定义方法的方法。|575443|575444|，有没有更好的方法来实现同样的功能？|575445|575446|575447|很难说清楚你到底想要实现什么。|575448|您可以使用您的方法创建一个module，并使用它extend所有对象。这将是最接近的类比。|575449|其他解决方案需要对代码进行更大规模的重构，例如使用Decorator+Design+Pattern，或者在您的特定Rails用例中使用Presenter。|575450|entityMap|0|LINK|mutability|MUTABLE|url|https://bugs.ruby-lang.org/issues/11665|1|http://c2.com/cgi/wiki?DecoratorPattern^0|0|0|0|0|0|8|3|H|3|P|3|V|3|17|3|1K|3|0|0|I|G|0|0|0|0|0|0|0|0|0|0|0|0|D|6|O|6|0|P|O|1|0^^$0|@$1|2|3|4|5|6|7|1P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1Q|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1R|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|1S|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|1T|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|1U|8|@$O|1V|P|1W|Q|R]|$O|1X|P|1Y|Q|R]|$O|1Z|P|20|Q|R]|$O|21|P|22|Q|R]|$O|23|P|24|Q|R]|$O|25|P|26|Q|R]]|9|@]|A|$]]|$1|S|3|T|5|6|7|27|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|28|8|@]|9|@$O|29|P|2A|1|2B]]|A|$]]|$1|W|3|-4|5|6|7|2C|8|@]|9|@]|A|$]]|$1|X|3|Y|5|Z|7|2D|8|@]|9|@]|A|$]]|$1|10|3|-4|5|6|7|2E|8|@]|9|@]|A|$]]|$1|11|3|-4|5|6|7|2F|8|@]|9|@]|A|$]]|$1|12|3|13|5|6|7|2G|8|@]|9|@]|A|$]]|$1|14|3|-4|5|6|7|2H|8|@]|9|@]|A|$]]|$1|15|3|16|5|Z|7|2I|8|@]|9|@]|A|$]]|$1|17|3|-4|5|6|7|2J|8|@]|9|@]|A|$]]|$1|18|3|-4|5|6|7|2K|8|@]|9|@]|A|$]]|$1|19|3|1A|5|6|7|2L|8|@]|9|@]|A|$]]|$1|1B|3|1C|5|6|7|2M|8|@$O|2N|P|2O|Q|R]|$O|2P|P|2Q|Q|R]]|9|@]|A|$]]|$1|1D|3|1E|5|6|7|2R|8|@]|9|@$O|2S|P|2T|1|2U]]|A|$]]|$1|1F|3|-4|5|6|7|2V|8|@]|9|@]|A|$]]]|1G|$1H|$5|1I|1J|1K|A|$1L|1M]]|1N|$5|1I|1J|1K|A|$1L|1O]]]]

Method definitions are code just like any other code. They can appear in methods just like any other code. And just like any other code, they will be executed every time the method runs.

So, this

<pre><code>class Foo
 def foo
 def bar
 end
 end
end
</code></pre>

is not a nested method, but simply a method that defines a method. It is easy to see that this is not a nested method, by simply calling it twice, paying attention to the warnings generated and inspecting the defined methods of the surrounding module:

<pre><code>foo = Foo.new

Foo.public_instance_methods(false)
#=&gt; [:foo]

foo.foo

Foo.public_instance_methods(false)
#=&gt; [:foo, :bar]

foo.foo
# (irb):3: warning: method redefined; discarding old bar
# (irb):3: warning: previous definition of bar was here
</code></pre>

As you can see, <code>bar</code> is not nested inside <code>foo</code>, instead it is defined besides <code>foo</code> in class <code>Foo</code>. It is only defined after <code>foo</code> has run, and it gets re-defined every time <code>foo</code> runs.

Your example is a bit different, of course, since it doesn't keep overwriting the method in the same class, instead it defines it in a different class every time it is called.

Note that there are plans of forbidding this kind of usage, see <a href="https://bugs.ruby-lang.org/issues/11665" rel="nofollow">Feature #11665: Support nested functions for better code organization</a>.

<blockquote>
 But what DO you call it?
</blockquote>

It's a method that defines a method.

<blockquote>
 And is there a better way to achieve the same functionality?
</blockquote>

It's kinda hard to tell what exactly it is you are trying to achieve.

You could create a <code>module</code> with your method and <code>extend</code> all the objects with it. That would be the closest analog.

Other solutions would require a larger restructuring of your code, e.g. using the <a href="http://c2.com/cgi/wiki?DecoratorPattern" rel="nofollow">Decorator Design Pattern</a> or, in your specific Rails use case, a Presenter.

I sometimes use this construct:

<pre><code>class Test
 def today
 date = Date.today

 def date.is_friday?
 strftime("%A") == "Friday"
 end

 date
 end
end
</code></pre>

it works fine...

<pre><code>t = Test.new
t.today # =&gt; &lt;Date: 2016-09-03 ((2457635j,0s,0n),+0s,2299161j)&gt;
t.today.is_friday? # =&gt; false
</code></pre>

I have always thought of this as a nested method. But others are adamant that Ruby does not have nested methods. OK, I'm not hooked on the name. But what DO you call it? And is there a better way to achieve the same functionality?

Ruby doesn't have nested methods, right? So what is this, and is there a better way?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有时会使用这个结构：class Test  def today    date = Date.today    def date.is_friday?      strftime("%A") == "Friday"    end    date  endend它工作得很好。t = Test.newt.today # ...

问Ruby没有嵌套的方法，对吧？那么这是什么，有没有更好的方法？
EN

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问Ruby没有嵌套的方法，对吧？那么这是什么，有没有更好的方法？EN