Safe Ruby Enum implementation
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This is a very basic implementation of enums in Ruby. The cornerstone of the library is safety.


Add this line to your application's Gemfile:

gem 'safe-enum'

And then execute:

$ bundle

Or install it yourself as:

$ gem install safe-enum


Define set of enums with code like this:

class Side < Enum::Base
  values :left, :right

Now get a value with the enum method safely defined values by argument with its Symbol or String type. If there is no defined such value Enum::TokenNotFoundError exception will be raised. And this is the safety - you will be noticed about the problem and fix it by introducing a new value or fixing a source of the invalid value. While others implementations of enums in Ruby (that I know) just silently ignore invalid values returning nil this one will raise the exception always. Example of usage:

Side.enum(:left) # => "left"
Side.enum('left') # => "left"
Side.enum(:invalid) # => Enum::TokenNotFoundError: token 'invalid'' not found in the enum Side
Side.enum('invalid') # => Enum::TokenNotFoundError: token 'invalid'' not found in the enum Side

Get all defined enum values with the all method:

Side.all # => ['left', 'rigth', 'whole']

Order or the returned values in the same as their definition. It's guaranteed.

In order to get array of defined enums safely use enums method:

 Side.enums(:left, :right) # => ['left', 'right']

If you have installed I18n in your application feel free to use name method to retreive the values' translations. For the given example the possible translation structure in yml format is the following:

      left: 'Left'
      right: 'Right'

The name method usage example: # => "Left"'left') # => "Left" # => "Right"'right') # => "Right" # => Enum::TokenNotFoundError: token 'invalid'' not found in the enum Side

If you don't have installed I18n in your project NameError exception will be raised on the name method call.

Consider the case when we have an object with a field with only enum values. Extend the class of this object by Enum::Predicates and use enumerize method to generate predicates. This is a more convenient way matching current value of the field with an enum value. Usage the predicate methods is safe also. It means that you can't pass to the method invalid enum value neither can have an invalid value in the field:

class Table
  extend Enum::Predicates

  attr_accessor :side

  enumerize :side, Side

@table =
@table.side_is?(:left) # => false
@table.side_is?(nil) # => false

@table.side = Side.enum(:left)
@table.side_is?(:left) # => true
@table.side_is?(:right) # => false
@table.side_is?(nil) # => false
@table.side_is?(:invalid) # => Enum::TokenNotFoundError: token 'invalid'' not found in the enum Side

@table.side = 'invalid'
@table.side_is?(nil) # => false
@table.side_is?(:left) # => Enum::TokenNotFoundError: token 'invalid'' not found in the enum Side
@table.side_any?(:left, :right) # => true
@table.side_any?(:right) # => false
@table.side_any?(:invalid, :left) # => Enum::TokenNotFoundError: token 'invalid'' not found in the enum Side

If you pass to the predicate nil or have nil value in the field the result will be always false. If you want to check that the field is nil just use Ruby's standard method nil?.

It's possible to get index of an enum value with index method. It can be convenient in some circumstances:

class WeekDay < Enum::Base
  values :sunday, :monday, :tuesday, :wednesday, :thusday, :friday, :saturday
WeekDay.index(:sunday) ==, 9, 13).wday # => true
WeekDay.index(:monday) # => 1
WeekDay.indexes # => [0, 1, 2, 3, 4, 5, 6]


After checking out the repo, run bin/setup to install dependencies. Then, run rake test 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 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.