C-style enums for ruby

This project is an attempt to provide c-style enums for ruby. It's obviously impossible (and not even desirable) to capture the exact syntax and semantics of c's enums in a ruby implementation, but the major capabilities and usage patterns are supported.

But ruby has symbols, why do we need enums?

Symbols are great. You should probably keep on using symbols in most of the places that you currently do. There are, however, certain situations that enums are better suited for. For instance:

• A variable can take on a finite set of known, named, values.

The set of values that a variable can take on define that variable's type. Rather than just scattering symbols throughout your code that modifes the variable, it is frequently helpful to encapsulate the type information in one place. An enum, being a lightweight, in-line class definition, is an ideal place to do this. Examples of this type of situation would be when you need to represent days-of-the-week or drink sizes available DayOfWeek = enum :sun, :mon, :tues, :wed, :thurs, :fri, :sat DrinkSize = enum :small, :medium, :large

• A dual name/value representation is needed. This is particularly common when you have a set of possible values with an inherent ordering.

Enums have the property of defining both names and values, so you can sometimes get the best of both worlds by using them. DrinkSize = enum :small, :medium, :large DrinkSize::SMALL < DrinkSize::LARGE # true

Basic Usage

require 'cenum'

class PetOwner

  Animals = enum :cat, :dog, :bird

  def initialize(animal)
    @animal = animal || Animals::DOG
  end

  def pet_says
    case @animal
      when Animals::CAT then 'meow'
      when Animals::DOG then 'woof'
      when Animals::BIRD then 'tweet'
    end
  end

end

bird_owner = PetOwner.new(PetOwner::Animals::BIRD)

bird_owner.pet_says  # 'tweet'

Features

• Enums contain a list of their values

  irb> Directions = enum :up, :down, :left, :right
  irb> Directions.values
  [:up, :down, :left, :right]
  

• Enum values map to integers

  irb> Directions::UP
  0
  irb> Directions::DOWN
  1
  

• Enum declaration is type declaration

  irb> Boolean = enum :true, :false
  irb> yes = Boolean.new(:true)
  irb> no = Boolean.new(:false)
  irb> yes == no
  false
  

• Value checks and mutators generated automatically

  irb> Boolean = enum :true, :false
  irb> yes = Boolean.new(:true)
  irb> no = Boolean.new(:false)
  irb> yes.true?
  true
  irb> no.true?
  false
  irb> maybe = Boolean.new(:true)
  irb> maybe == yes
  true
  irb> maybe.false!
  irb> maybe == yes
  false
  irb> maybe == no
  true
  

• Direct comparison of type instances with value names

  irb> Boolean = enum :true, :false
  irb> yes = Boolean.new(:true)
  irb> yes == Boolean::TRUE
  true
  irb> yes != Boolean::FALSE
  true
  

• Values can be compared

  irb> up = Directions.new(:up)
  irb> down = Directions.new(:down)
  irb> up < down
  true
  

• Values can be compared to their names

  irb> up == :up
  true
  

• Custom value mappings

  irb> Drinks = enum :small, :medium, :large, :infinite => -1
  irb> Drinks::SMALL
  0
  irb> Drinks::MEDIUM
  1
  irb> Drinks::INFINITE
  -1
  

Roadmap

• Improve custom value mappings
  • Spec
  • Prevent collisions
  • Allow non-integer value mappings
  • Consider using a DSL to improve syntax (gets messy in some cases currently)
• Convert to Gem