Compare By

A better version of Ruby's Comparable.


Add this line to your application's Gemfile:

gem 'compare_by'

And then execute:

$ bundle

Or install it yourself as:

$ gem install compare_by


Suppose you have the following class:

class SomeClass
  attr_accessor :some_attr, :some_other_attr

  # ...

To ensure the uniqueness of each instance of the class, include the CompareBy module and specify which attribute(s)/method(s) you want the instances compared by.

require 'compare_by'

class SomeClass
  include CompareBy

  attr_accessor :some_attr, :some_other_attr
  compare_by :some_attr

  # ...

If you then made two instances of SomeClass with the same value of some_attr, they would be considered equivalent.

instance1 =
instance1.some_attr = 'foo'
instance2 =
instance2.some_attr = 'foo'

instance1 == instance2 #=> true
instance1.eql?(instance2) #=> true
[instance1, instance2].uniq #=> [instance1]

Note that you can specify one or more attribute(s)/method(s) for instances to be compared by, and each will be considered in order.


After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at[USERNAME]/compare_by. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.


The gem is available as open source under the terms of the MIT License.