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Friendly enum type system for Ruby
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README.md

MetaEnum

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

Installation

Add this line to your application's Gemfile:

gem 'meta_enum'

And then execute:

$ bundle

Or install it yourself as:

$ gem install meta_enum

Usage

Create a enum type:

require 'meta_enum'

ColorType = MetaEnum::Type.new(red: 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
v.name # => :red

Values can have extra associated data.

AgeType = MetaEnum::Type.new(child: [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 MetaEnum::Type.new. For example, to use string values:

CardType = MetaEnum::Type.new({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 = MetaEnum::Type.new(
  {
    child: [0, {description: "Less than 18", range: 0...18}],
    adult: [1, {description: "At least 18", range: 18...Float::INFINITY}]
  },
  element_class: Class.new(MetaEnum::Element) {
    def description
      data[:description]
    end

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

Development

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 rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ccsalespro/meta_enum.

License

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

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