Including a Ruby class from a separate file

Question

For a while I had been including an entire class inside of a Ruby module. Apparently this is not what I am supposed to do. It appears that the point of a module is to store functions which can then be included as methods in a new class.

I don't want this. I have a class that I want to keep in a separate file which I can access from other files. How can I do this?

Thanks.

Solution

Modules serve a dual purpose as a holder for functions and as a namespace. Keeping classes in modules is perfectly acceptable. To put a class in a separate file, just define the class as usual and then in the file where you wish to use the class, simply put require 'name_of_file_with_class' at the top. For instance, if I defined class Foo in foo.rb, in bar.rb I would have the line require 'foo'.

If you are using Rails, this include often happens automagically

Edit: clarification of file layout

#file: foo.rb
class Foo
  def initialize
    puts "foo"
  end
end

...

#file: bar.rb
require 'foo'

Foo.new

If you are in Rails, put these classes in lib/ and use the naming convention for the files of lowercase underscored version of the class name, e.g. Foo -> foo.rb, FooBar -> foo_bar.rb, etc.

As of ruby version 1.9 you can use require_relative, to require files relatively to the file you are editing.

Comments

[Dirk]

This post clarifies the require_relative expression in case you are running into problems with the above example when on Ruby >=1.9.2 Ruby require_relative example

[user94154]

thanks, very helpful. could you clarify that last sentence? it seems you may have had a typo(?). If class foo is stored in bar.rb, i require 'foo' in bazcontroller.rb? Then foo.new is usable in bazcontroller.rb?

[boutta]

Maybe it would be nice to add some info on 'require_relative' for Ruby 1.9 since the code doesn't work for this version.

[DorkRawk]

@boutta Thank you for the 1.9 clarification, this fixed my issue.

[mj_]

Answer saved the say for me. I had a class "SendGridHelper" in a file called "app/lib/sendgrid_helper.rb" I had to change the file name to "app/lib/send_grid_helper.rb".