Re: Ruby idiom for enum?

David Brady wrote:

In C++, I would use an enum for each of the values, then build arrays of floats and strings indexed by those enums to hold the thresholds and descriptions.

That's also possible in Ruby, but I think it is a better idea to aggregate all the data into the enum member itself.

Here's Ruby code for doing C++ style enums:

# Represents a C# style enumeration of known values.
#
# Usage:
#   Color = Enum.new(:Red, :Green, :Blue)
#   Color.is_a?(Enum) # => true
#   Color::Red.inspect # => "Color::Red"
#   Color::Green.is_a?(Color) # => true
#   Color::Green.is_a?(Enum::Member) # => true
#   Color::Green.index # => 1
#   Color::Blue.enum # => Color
#   values = [[255, 0, 0], [0, 255, 0], [0, 0, 255]]
#   values[Color::Green] # => [0, 255, 0]
#   Color[0] # => Color::Red
#   Color.size # => 3
#
# Enums are enumerable. Enum::Members are comparable.
class Enum < Module
  class Member < Module
    attr_reader :enum, :index

    def initialize(enum, index)
      @enum, @index = enum, index
      # Allow Color::Red.is_a?(Color)
      extend enum
    end

    # Allow use of enum members as array indices
    alias :to_int :index
    alias :to_i :index

    # Allow comparison by index
    def <=>(other)
      @index <=> other.index
    end

    include Comparable
  end

  def initialize(*symbols, &block)
    @members = []
    symbols.each_with_index do |symbol, index|
      # Allow Enum.new(:foo)
      symbol = symbol.to_s.sub(/^[a-z]/) { |letter| letter.upcase }.to_sym
      member = Enum::Member.new(self, index)
      const_set(symbol, member)
      @members << member
    end
    super(&block)
  end

  def [](index) @members[index] end
  def size() @members.size end
  alias :length :size

  def first(*args) @members.first(*args) end
  def last(*args) @members.last(*args) end

  def each(&block) @members.each(&block) end
  include Enumerable
end


But I think it is not the best match in this case.

Struct.new("RatingData", name, threshold, description)

RATING_GOOD = Struct::RatingData( :Good, 0.8, "Good Rating" )
RATING_FAIR = Struct::RatingData( :Fair, 0.5, "Fair Rating" )


This sounds good, but I'd go with a module:

module Rating
  Good = Struct::RatingData.new(:Good, 0.8, "Good Rating")
  Fair = Struct::RatingData.new(:Fair, 0.5, "Fair Rating")
end

That seems more Rubyish to me.



.

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