Ruby Comparable and Range!

comparable.rb

# I was familiar with this, the keys here are "include Comparable" and the <=> method.
# <=> return 1 for larger, 0 for equal, -1 for smaller than "other"

class UndergradClassification
  include Comparable

  CLASSIFICATIONS = ["freshman", "sophomore", "junior", "senior"]

  attr_reader :name, :index
  def initialize(name)
    @name = name
    @index = CLASSIFICATIONS.index(name)
  end

  def <=>(other)
    index <=> other.index
  end
end

UndergradClassification.new("junior") > UndergradClassification.new("senior")  # false
UndergradClassification.new("junior") < UndergradClassification.new("senior")  # true
UndergradClassification.new("junior") <= UndergradClassification.new("junior") # true

range.rb

# By adding succ we can support ruby Ranges! 
# https://ruby-doc.org/3.2.2/Range.html

class UndergradClassification
  include Comparable

  CLASSIFICATIONS = ["freshman", "sophomore", "junior", "senior"]

  attr_reader :name, :index
  def initialize(name)
    @name = name
    @index = CLASSIFICATIONS.index(name)
  end

  def succ
    next_up = CLASSIFICATIONS[index + 1]

    raise RangeError.new unless next_up

    self.class.new(next_up)
  end

  def <=>(other)
    index <=> other.index
  end
end

# Inclusive, two dots
(UndergradClassification.new("freshman") .. UndergradClassification.new("senior")).collect do |classification|
  classification.name
end # ["freshman", "sophomore", "junior", "senior"]

# Exclusive, three dots
(UndergradClassification.new("freshman") ... UndergradClassification.new("senior")).collect do |classification|
  classification.name
end # ["freshman", "sophomore", "junior"]

(UndergradClassification.new("freshman") .. UndergradClassification.new("senior")).include?(UndergradClassification.new("senior")) # true
(UndergradClassification.new("freshman") .. UndergradClassification.new("junior")).include?(UndergradClassification.new("senior")) # false