Where to define custom error types in Ruby and/or Rails?

Question

Is there a best practice for defining custom error types in a Ruby library (gem) or Ruby on Rails application? Specifically:

1. Where do they belong structurally

Answer 1

To ensure that autoloading works as expected in Rails 4.1.10 for multiple custom error classes, you'll want to specify separate files for each. This should work in development with its dynamically reloading.

This is how I setup errors in a recent project:

In lib/app_name/error/base.rb

module AppName
    module Error
        class Base < StandardError; end
    end
end

and in subsequent custom errors, like in lib/app_name/error/bad_stuff.rb

module AppName
    module Error
        class BadStuff < ::AppName::Error::Base; end
    end
end

You should then be able to call your errors via:

 raise AppName::Error::BadStuff.new("Bad stuff just happened")