How do I convert a Ruby class name to a underscore-delimited symbol?

How can I programmatically turn a class name, `FooBar`, into a symbol, `:foo_bar`? e.g. something like this, but that handles camel case properly?

FooBar.to_s.downcase.to_sym

**Rails 4 `.model_name`**

In Rails 4, it returns an [`ActiveModel::Name`](

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) object which contains many useful more "semantic" attributes such as:

FooBar.model_name.param_key
#=> "foo_bar"

FooBar.model_name.route_key
#=> "foo_bars"

FooBar.model_name.human
#=> "Foo bar"

So you should use one of those if they match your desired meaning, which is likely the case. Advantages:

- easier to understand your code
- your app will still work even in the (unlikely) event that Rails decides to change a naming convention.

BTW, `human` has the advantage of being I18N aware.

Here's what I went for:

module MyModule
module ClassMethods
def class_to_sym
name_without_namespace = name.split("::").last
name_without_namespace.gsub(/([^\^])([A-Z])/,'\1_\2').downcase.to_sym
end
end

def self.included(base)
base.extend(ClassMethods)
end
end

class ThisIsMyClass
include MyModule
end

ThisIsMyClass.class_to_sym #:this_is_my_class

Rails comes with a method called `underscore` that will allow you to transform CamelCased strings into underscore_separated strings. So you might be able to do this:

FooBar.name.underscore.to_sym

But you will have to install ActiveSupport just to do that, as ipsum says.

If you don't want to install ActiveSupport just for that, you can monkey-patch `underscore` into `String` yourself (the underscore function is defined in [ActiveSupport::Inflector][1]):

class String
def underscore
word = self.dup
word.gsub!(/::/, '/')
word.gsub!(/([A-Z]+)([A-Z][a-z])/,'\1_\2')
word.gsub!(/([a-z\d])([A-Z])/,'\1_\2')
word.tr!("-", "_")
word.downcase!
word
end
end


[1]:

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first: gem install activesupport

require 'rubygems'
require 'active_support'
"FooBar".underscore.to_sym