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MetaEnum is a library for handling enum types in Ruby. It makes it easy to convert between external values and internal names.


Add this line to your application's Gemfile:

gem 'meta_enum'

And then execute:

$ bundle

Or install it yourself as:

$ gem install meta_enum


Create a enum type:

require 'meta_enum'

ColorType = 0, green: 1, blue: 2)

Use the [] operator to lookup a value by name:

ColorType[:green] # => #<MetaEnum::Element: 1 => green}>

Or lookup by number:

ColorType[1] # => #<MetaEnum::Element: 1 => green}>

Elements can also be easily compared with values or names:

ColorType[:green] == 1 # => true
ColorType[:green] == :green # => true

Missing names would almost always be a programming error, so that will raise an exception.

ColorType[:purple] # => raises: KeyError: key not found: :purple

But missing values could mean that there are values defined externally we do not know about. So it is preferable not to raise an exception.

ColorType[42] # => #<MetaEnum::MissingElement: 42}>

Value and name can be retrieved from a MetaEnum::Element

v = ColorType[:red] # => #<MetaEnum::Element: 0 => red}>
v.value # => 0 # => :red

Values can have extra associated data.

AgeType = [0, "Less than 18"], adult: [1, "At least 18"])
AgeType[:child].data # => "Less than 18"

Non-integer values can be enabled by passing a value_normalizer to For example, to use string values:

CardType ={visa: "VS", mastercard: "MC", discover: "DS"}, value_normalizer: method(:String))
CardType[:visa] # => #<MetaEnum::Element: visa: "VS", data: nil>
CardType["VS"] # => #<MetaEnum::Element: visa: "VS", data: nil>
CardType["VS"].value # => "VS"

The class used to create the elements can be customized with the element_class argument.

AgeType =
    child: [0, {description: "Less than 18", range: 0...18}],
    adult: [1, {description: "At least 18", range: 18...Float::INFINITY}]
  element_class: {
    def description

    def range
AgeType[:child].description # => "Less than 18"
AgeType[:child].range # => 0...18


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


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