blocks|key|994658|text|如果你想要一些简单的东西来处理你的特殊情况，你可以这样写|type|unstyled|depth|inlineStyleRanges|entityRanges|data|994659|Object.const_get("Admin").const_get("MetaDatasController")|code-block|syntax|javascript|994660|但是如果你想要更通用的东西，在::上拆分字符串，然后一个接一个地解析名称：|offset|length|style|CODE|994661|def+class_from_string(str)
++str.split('::').inject(Object)+do+%7Cmod,+class_name%7C
++++mod.const_get(class_name)
++end
end

the_class+=+class_from_string("Admin::MetaDatasController")|994662|在第一次迭代中，要求Object提供常量Admin并返回Admin模块或类，然后在第二次迭代中要求该模块或类提供常量MetaDatasController，并返回该类。由于没有更多的组件，该类将从方法中返回(如果有更多的组件，它将进行迭代，直到找到最后一个组件)。|994663|entityMap^0|0|0|F|2|0|0|A|6|K|5|S|5|1M|J|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@$I|V|J|W|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|Y|8|@$I|Z|J|10|K|L]|$I|11|J|12|K|L]|$I|13|J|14|K|L]|$I|15|J|16|K|L]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|R|$]]

If you want something simple that handles just your special case you can write

<pre><code>Object.const_get("Admin").const_get("MetaDatasController")
</code></pre>

But if you want something more general, split the string on <code>::</code> and resolve the names one after the other:

<pre><code>def class_from_string(str)
 str.split('::').inject(Object) do |mod, class_name|
 mod.const_get(class_name)
 end
end

the_class = class_from_string("Admin::MetaDatasController")
</code></pre>

On the first iteration <code>Object</code> is asked for the constant <code>Admin</code> and returns the <code>Admin</code> module or class, then on the second iteration that module or class is asked for the constant <code>MetaDatasController</code>, and returns that class. Since there are no more components that class is returned from the method (if there had been more components it would have iterated until it found the last).

blocks|key|994704|text|我可能是大错特错，但是eval不会返回这个类吗？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|994705|eval("Admin::MetaDatasController")|code-block|syntax|javascript|994706|因此，eval("Admin::MetaDatasController").new将与Admin::MetaDatasController.new相同|offset|length|style|CODE|994707|entityMap^0|0|0|3|12|17|U|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]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]|$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|N|$]]

i could be way off-base, but wouldn't eval return the class?

<pre><code>eval("Admin::MetaDatasController")
</code></pre>

so <code>eval("Admin::MetaDatasController").new</code> would be the same as <code>Admin::MetaDatasController.new</code>

blocks|key|1209060|text|ActiveSupport提供了一个名为constantize的方法，它可以做到这一点。如果您在Rails上，我假设您是基于常量的名称，那么您已经加载了ActiveSupport。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1209061|require+'active_support/core_ext/string'

class+Admin
++class+MetaDatasController
++end
end

"Admin::MetaDatasController".constantize+#+=>+Admin::MetaDatasController|code-block|syntax|javascript|1209062|要查看该方法是如何实现的，请查看https://github.com/rails/rails/blob/85c2141fe3d7edb636a0b5e1d203f05c70db39dc/activesupport/lib/active_support/inflector/methods.rb#L230-L253|offset|length|1209063|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/rails/rails/blob/85c2141fe3d7edb636a0b5e1d203f05c70db39dc/activesupport/lib/active_support/inflector/methods.rb#L230-L253^0|0|0|G|3W|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

ActiveSupport provides a method called constantize, which will do this. If you are on Rails, which I assume you are based on the name of your constant, then you already have ActiveSupport loaded. 

<pre><code>require 'active_support/core_ext/string'

class Admin
 class MetaDatasController
 end
end

"Admin::MetaDatasController".constantize # =&gt; Admin::MetaDatasController
</code></pre>

To see how the method is implemented, check out <a href="https://github.com/rails/rails/blob/85c2141fe3d7edb636a0b5e1d203f05c70db39dc/activesupport/lib/active_support/inflector/methods.rb#L230-L253" rel="noreferrer">https://github.com/rails/rails/blob/85c2141fe3d7edb636a0b5e1d203f05c70db39dc/activesupport/lib/active_support/inflector/methods.rb#L230-L253</a>

blocks|key|1209196|text|在Ruby+2.x中，你可以这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1209197|Object.const_get('Admin::MetaDatasController')
=>+Admin::MetaDatasController|code-block|syntax|javascript|1209198|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|$]]

In Ruby 2.x, you can just do this:

<pre><code>Object.const_get('Admin::MetaDatasController')
=&gt; Admin::MetaDatasController
</code></pre>

Having a string with the module and name of a class, like:

<pre><code>"Admin::MetaDatasController"
</code></pre>

how do I get the actual class?

The following code works if there's no module:

<pre><code>Kernel.const_get("MetaDatasController")
</code></pre>

but it breaks with the module:

<pre><code>ruby-1.8.7-p174 &gt; Kernel.const_get("Admin::MetaDatasController")
NameError: wrong constant name Admin::MetaDatasController
 from (irb):34:in `const_get'
 from (irb):34
ruby-1.8.7-p174 &gt; 
</code></pre>

Get a class by name in Ruby?

Kernel

具有包含模块和类名的字符串，如下所示："Admin::MetaDatasController"如何获取实际的类？如果没有模块，下面的代码可以工作：Kernel.const_get("MetaDatasController")但它与模块断开了：ruby-1.8.7-p174 > Kernel.const_get("Adm...

问在Ruby中按名称获取类？
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