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 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):

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

Rails 4 .model_name

In Rails 4, it returns an ActiveModel::Name 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.

first: gem install activesupport

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

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