blocks|key|1310892|text|重写名为inherited的类方法。此方法将在创建时传递给您可以跟踪的子类。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1310893|entityMap|0|LINK|mutability|MUTABLE|url|http://ruby-doc.org/core-1.9.3/Class.html#method-i-inherited^0|4|9|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

Override the class method named <a href="http://ruby-doc.org/core-1.9.3/Class.html#method-i-inherited" rel="noreferrer">inherited</a>. This method would be passed the subclass when it is created which you can track.

blocks|key|1095775|text|下面是一个示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1095776|class+Parent
++def+self.descendants
++++ObjectSpace.each_object(Class).select+{+%7Cklass%7C+klass+<+self+}
++end
end

class+Child+<+Parent
end

class+GrandChild+<+Child
end

puts+Parent.descendants
puts+Child.descendants|code-block|syntax|javascript|1095777|puts+Parent.descendants为您提供：|1095778|GrandChild
Child|1095779|puts+Child.descendants为您提供：|1095780|GrandChild|1095781|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

Here is an example:

<pre><code>class Parent
 def self.descendants
 ObjectSpace.each_object(Class).select { |klass| klass &lt; self }
 end
end

class Child &lt; Parent
end

class GrandChild &lt; Child
end

puts Parent.descendants
puts Child.descendants
</code></pre>

puts Parent.descendants gives you:

<pre><code>GrandChild
Child
</code></pre>

puts Child.descendants gives you:

<pre><code>GrandChild
</code></pre>

blocks|key|1310972|text|带有漂亮的链式迭代器的Ruby+1.9+(或1.8.7)：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1310973|#!/usr/bin/env+ruby1.9

class+Class
++def+descendants
++++ObjectSpace.each_object(::Class).select+{%7Cklass%7C+klass+<+self+}
++end
end|code-block|syntax|javascript|1310974|Ruby+1.8.7之前版本：|1310975|#!/usr/bin/env+ruby

class+Class
++def+descendants
++++result+=+[]
++++ObjectSpace.each_object(::Class)+{%7Cklass%7C+result+<<+klass+if+klass+<+self+}
++++result
++end
end|1310976|像这样使用它：|1310977|#!/usr/bin/env+ruby

p+Animal.descendants|1310978|entityMap|0|LINK|mutability|MUTABLE|url|http://ruby-lang.org/^0|B|4|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@$A|Z|B|10|1|11]]|C|$]]|$1|D|3|E|5|F|7|12|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|13|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|14|8|@]|9|@]|C|$G|H]]|$1|M|3|N|5|6|7|15|8|@]|9|@]|C|$]]|$1|O|3|P|5|F|7|16|8|@]|9|@]|C|$G|H]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]]]

<a href="http://Ruby-Lang.Org/" rel="noreferrer">Ruby</a> 1.9 (or 1.8.7) with nifty chained iterators:

<pre><code>#!/usr/bin/env ruby1.9

class Class
 def descendants
 ObjectSpace.each_object(::Class).select {|klass| klass &lt; self }
 end
end
</code></pre>

Ruby pre-1.8.7:

<pre><code>#!/usr/bin/env ruby

class Class
 def descendants
 result = []
 ObjectSpace.each_object(::Class) {|klass| result &lt;&lt; klass if klass &lt; self }
 result
 end
end
</code></pre>

Use it like so:

<pre><code>#!/usr/bin/env ruby

p Animal.descendants
</code></pre>

blocks|key|1095889|text|或者(为ruby+1.9%2B更新)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1095890|ObjectSpace.each_object(YourRootClass.singleton_class)|code-block|syntax|javascript|1095891|Ruby+1.8兼容方式：|1095892|ObjectSpace.each_object(class<<YourRootClass;self;end)|1095893|请注意，这不适用于模块。此外，答案中还将包括YourRootClass。您可以使用Array#-或其他方法来删除它。|1095894|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Alternatively (updated for ruby 1.9+):

<pre><code>ObjectSpace.each_object(YourRootClass.singleton_class)
</code></pre>

Ruby 1.8 compatible way:

<pre><code>ObjectSpace.each_object(class&lt;&lt;YourRootClass;self;end)
</code></pre>

Note that this won't work for modules. Also, YourRootClass will be included in the answer. You can use Array#- or another way to remove it.

blocks|key|1311133|text|Rails为每个对象提供了一个子类方法，但是它没有很好的文档记录，我也不知道它是在哪里定义的。它以字符串的形式返回类名的数组。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1311134|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Rails provides a subclasses method for every object, but it's not well documented, and I don't know where it's defined. It returns an array of class names as strings.

blocks|key|1095995|text|Ruby+Facets有Class#descendants，|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1095996|require+'facets/class/descendants'|code-block|syntax|javascript|1095997|它还支持分代距离参数。|1095998|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Ruby Facets has Class#descendants,

<pre><code>require 'facets/class/descendants'
</code></pre>

It also supports a generational distance parameter.

blocks|key|1311217|text|如果您使用Rails+>=+3，则有两个选项。如果需要多个级别的子类深度，请使用.descendants，或者对第一级的子类使用.subclasses。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1311218|示例：|1311219|class+Animal
end

class+Mammal+<+Animal
end

class+Dog+<+Mammal
end

class+Fish+<+Animal
end

Animal.subclasses+#=>+[Mammal,+Fish]+
Animal.descendants++#=>+[Dog,+Mammal,+Fish]|code-block|syntax|javascript|1311220|entityMap|0|LINK|mutability|MUTABLE|url|http://apidock.com/rails/Class/descendants|1|http://apidock.com/rails/v3.2.13/Class/subclasses^0|14|C|1S|B|14|C|0|1S|B|1|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@$9|11|A|12|1|13]|$9|14|A|15|1|16]]|E|$]]|$1|F|3|G|5|6|7|17|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|18|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]|U|$5|P|Q|R|E|$S|V]]]]

If you use Rails >= 3, you have two options in place. Use <a href="http://apidock.com/rails/Class/descendants"><code>.descendants</code></a> if you want more than one level depth of children classes, or use <a href="http://apidock.com/rails/v3.2.13/Class/subclasses"><code>.subclasses</code></a> for the first level of child classes.

Example: 

<pre><code>class Animal
end

class Mammal &lt; Animal
end

class Dog &lt; Mammal
end

class Fish &lt; Animal
end

Animal.subclasses #=&gt; [Mammal, Fish] 
Animal.descendants #=&gt; [Dog, Mammal, Fish]
</code></pre>

blocks|key|1311274|text|您可以使用require+'active_support/core_ext'并使用descendants方法。Check+out+the+doc，并在IRB或pry中尝试一下。可以在没有Rails的情况下使用。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1311275|entityMap|0|LINK|mutability|MUTABLE|url|http://edgeguides.rubyonrails.org/active_support_core_extensions.html^0|5|X|15|B|1J|H|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]|$9|Q|A|R|B|C]]|D|@$9|S|A|T|1|U]]|E|$]]|$1|F|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

You can <code>require 'active_support/core_ext'</code> and use the <code>descendants</code> method. <a href="http://edgeguides.rubyonrails.org/active_support_core_extensions.html" rel="nofollow">Check out the doc</a>, and give it a shot in IRB or pry. Can be used without Rails.

blocks|key|1096133|text|使用descendants_tracker+gem可能会有所帮助。以下示例是从gem的文档中复制的：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1096134|class+Foo
++extend+DescendantsTracker
end

class+Bar+<+Foo
end

Foo.descendants+#+=>+[Bar]|code-block|syntax|javascript|1096135|这个gem是由流行的virtus+gem使用的，所以我认为它非常可靠。|1096136|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/dkubb/descendants_tracker|1|https://github.com/solnic/virtus^0|2|N|0|0|0|A|A|1|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@$A|10|B|11|1|12]]|C|$]]|$1|K|3|-4|5|6|7|13|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]|S|$5|N|O|P|C|$Q|T]]]]

Using <a href="https://github.com/dkubb/descendants_tracker" rel="nofollow">descendants_tracker gem</a> may help. The following example is copied from the gem's doc:

<pre><code>class Foo
 extend DescendantsTracker
end

class Bar &lt; Foo
end

Foo.descendants # =&gt; [Bar]
</code></pre>

This gem is used by the popular <a href="https://github.com/solnic/virtus" rel="nofollow">virtus gem</a>, so I think it's pretty solid.

blocks|key|1311395|text|尽管使用ObjectSpace可以正常工作，但继承的类方法似乎更适合inherited(subclass)+Ruby+documentation+|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1311396|Objectspace本质上是一种访问当前使用已分配内存的任何内容的方法，因此迭代它的每个元素以检查它是否是Animal类的子类并不理想。|1311397|在下面的代码中，继承的Animal类方法实现了一个回调，该回调将把任何新创建的子类添加到它的后代数组中。|1311398|class+Animal
++def+self.inherited(subclass)
++++@descendants+=+[]
++++@descendants+<<+subclass
++end

++def+self.descendants
++++puts+@descendants+
++end
end|code-block|syntax|javascript|1311399|entityMap|0|LINK|mutability|MUTABLE|url|http://ruby-doc.org/core-2.3.0/Class.html#method-i-inherited^0|Y|13|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|Z|8|@]|9|@]|C|$]]|$1|H|3|I|5|J|7|10|8|@]|9|@]|C|$K|L]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

Although using ObjectSpace works, the inherited class method seems to be better suitable here <a href="http://ruby-doc.org/core-2.3.0/Class.html#method-i-inherited" rel="noreferrer">inherited(subclass) Ruby documentation </a> 

Objectspace is essentially a way to access anything and everything that's currently using allocated memory, so iterating over every single one of its elements to check if it is a sublass of the Animal class isn't ideal. 

In the code below, the inherited Animal class method implements a callback that will add any newly created subclass to its descendants array.

<pre><code>class Animal
 def self.inherited(subclass)
 @descendants = []
 @descendants &lt;&lt; subclass
 end

 def self.descendants
 puts @descendants 
 end
end
</code></pre>

blocks|key|1311436|text|此方法将返回一个对象的所有子对象的多维散列。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1311437|def+descendants_mapper(klass)
++klass.subclasses.reduce({}){+%7Cmemo,+subclass%7C
++++memo[subclass]+=+descendants_mapper(subclass);+memo
++}
end

{+MasterClass+=>+descendants_mapper(MasterClass)+}|code-block|syntax|javascript|1311438|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This method will return a multidimensional hash of all of an Object's descendants.

<pre><code>def descendants_mapper(klass)
 klass.subclasses.reduce({}){ |memo, subclass|
 memo[subclass] = descendants_mapper(subclass); memo
 }
end

{ MasterClass =&gt; descendants_mapper(MasterClass) }
</code></pre>

blocks|key|1311480|text|一个简单的版本，它给出了一个类的所有后代的数组：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1311481|def+descendants(klass)
++all_classes+=+klass.subclasses
++(all_classes+%2B+all_classes.map+{+%7Cc%7C+descendants(c)+}.reject(&:empty?)).flatten
end|code-block|syntax|javascript|1311482|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

A simple version that give an array of all the descendants of a class:

<pre><code>def descendants(klass)
 all_classes = klass.subclasses
 (all_classes + all_classes.map { |c| descendants(c) }.reject(&amp;:empty?)).flatten
end
</code></pre>

blocks|key|1096461|text|基于其他答案(特别是那些推荐subclasses和descendants的答案)，您可能会发现在Rails.env.development中，事情变得令人困惑。这是由于在开发过程中(默认情况下)关闭了预加载。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1096462|如果你在rails+console中胡闹，你只需要命名这个类，它就会被加载。从那时起，它将在subclasses中显示出来。|1096463|在某些情况下，您可能需要在代码中强制加载类。对于单表继承(+Single+Table+Inheritance，STI)尤其如此，在这种情况下，您的代码很少直接提到子类。我遇到过一两种情况，我不得不迭代所有的STI子类……这在开发中并不能很好地工作。|1096464|以下是我加载这些类的技巧，仅用于开发：|1096465|if+Rails.env.development?
++##+These+are+required+for+STI+and+subclasses()+to+eager+load+in+development:
++require_dependency+Rails.root.join('app',+'models',+'color',+'green.rb')
++require_dependency+Rails.root.join('app',+'models',+'color',+'blue.rb')
++require_dependency+Rails.root.join('app',+'models',+'color',+'yellow.rb')
end|code-block|syntax|javascript|1096466|在此之后，子类按预期工作：|1096467|>+Color.subclasses
=>+[Color::Green,+Color::Blue,+Color::Yellow]|1096468|请注意，这在生产中不是必需的，因为所有类都是预先加载的。|1096469|是的，这里有各种各样的代码味道。不管你要不要，it...it允许你在开发过程中不再急切地加载，同时仍然执行动态的类操作。一旦进入prod，这不会对性能产生任何影响。|1096470|entityMap^0|E|A|P|B|0|4|D|1A|A|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|15|8|@$9|16|A|17|B|C]|$9|18|A|19|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1A|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|1B|8|@]|D|@]|E|$]]|$1|L|3|M|5|N|7|1C|8|@]|D|@]|E|$O|P]]|$1|Q|3|R|5|6|7|1D|8|@]|D|@]|E|$]]|$1|S|3|T|5|N|7|1E|8|@]|D|@]|E|$O|P]]|$1|U|3|V|5|6|7|1F|8|@]|D|@]|E|$]]|$1|W|3|X|5|6|7|1G|8|@]|D|@]|E|$]]|$1|Y|3|-4|5|6|7|1H|8|@]|D|@]|E|$]]]|Z|$]]

Building on other answers (particularly those recommending <code>subclasses</code> and <code>descendants</code>), you may find that in Rails.env.development, things get confusing. This is due to eager loading turned off (by default) in development.
If you're fooling around in <code>rails console</code>, you can just name the class, and it will be loaded. From then on out, it will show up in <code>subclasses</code>.
In some situations, you may need to force the loading of classes in code. This is particularly true of Single Table Inheritance (STI), where your code rarely mentions the subclasses directly. I've run into one or two situations where I had to iterate all the STI subclasses ... which does not work very well in development.
Here's my hack to load just those classes, just for development:
<pre><code>if Rails.env.development?
 ## These are required for STI and subclasses() to eager load in development:
 require_dependency Rails.root.join('app', 'models', 'color', 'green.rb')
 require_dependency Rails.root.join('app', 'models', 'color', 'blue.rb')
 require_dependency Rails.root.join('app', 'models', 'color', 'yellow.rb')
end
</code></pre>
After that, subclasses work as expected:
<pre><code>&gt; Color.subclasses
=&gt; [Color::Green, Color::Blue, Color::Yellow]
</code></pre>
Note that this is not required in production, as all classes are eager loaded up front.
And yes, there's all kinds of code smell here. Take it or leave it...it allows you to leave eager loading off in development, while still exercising dynamic class manipulation. Once in prod, this has no performance impact.

blocks|key|1096575|text|计算任意类的传递外壳|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1096576|def+descendants(parent:+Object)
+++++outSet+=+[]
+++++lastLength+=+0
+++++
+++++outSet+=+ObjectSpace.each_object(Class).select+{+%7Cchild%7C+child+<+parent+}
+++++
+++++return+if+outSet.empty?
+++++
+++++while+outSet.length+==+last_length
+++++++temp+=+[]
+++++++last_length+=+outSet.length()
+++++++
+++++++outSet.each+do+%7Cparent%7C
++++++++temp+=+ObjectSpace.each_object(Class).select+{+%7Cchild%7C+child+<+parent+}
+++++++end
+++++++
+++++++outSet.concat+temp
+++++++outSet.uniq
+++++++temp+=+nil
+++++end
+++++outSet
+++++end
+++end|code-block|syntax|javascript|1096577|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

To compute the transitive hull of an arbitrary class
<pre><code>def descendants(parent: Object)
 outSet = []
 lastLength = 0
 
 outSet = ObjectSpace.each_object(Class).select { |child| child &lt; parent }
 
 return if outSet.empty?
 
 while outSet.length == last_length
 temp = []
 last_length = outSet.length()
 
 outSet.each do |parent|
 temp = ObjectSpace.each_object(Class).select { |child| child &lt; parent }
 end
 
 outSet.concat temp
 outSet.uniq
 temp = nil
 end
 outSet
 end
 end
</code></pre>

I can easily ascend the class hierarchy in Ruby:

<pre><code>String.ancestors # [String, Enumerable, Comparable, Object, Kernel]
Enumerable.ancestors # [Enumerable]
Comparable.ancestors # [Comparable]
Object.ancestors # [Object, Kernel]
Kernel.ancestors # [Kernel]
</code></pre>

Is there any way to descend the hierarchy as well? I'd like to do this

<pre><code>Animal.descendants # [Dog, Cat, Human, ...]
Dog.descendants # [Labrador, GreatDane, Airedale, ...]
Enumerable.descendants # [String, Array, ...]
</code></pre>

but there doesn't seem to be a <code>descendants</code> method.

(This question comes up because I want to find all the models in a Rails application that descend from a base class and list them; I have a controller that can work with any such model and I'd like to be able to add new models without having to modify the controller.)

Look up all descendants of a class in Ruby

Kernel

我可以很容易地在Ruby中提升类层次结构：String.ancestors     # [String, Enumerable, Comparable, Object, Kernel]Enumerable.ancestors # [Enumerable]Comparable.ancestors # [Comparabl...

问查找Ruby中某个类的所有后代
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问查找Ruby中某个类的所有后代
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