Comparing items based on their index in an array in Ruby

I have a Card class and I want to overload the > operator to compare against another card (Ace is higher than king, king higher than queen, etc). I've forgotten what little I ever knew about Ruby and don't have a clue where to start.

class Card
  @@RANKS = ['A', 'K', 'Q', 'J', 'T', '9', '8','7','6','5','4','3','2']
  attr_reader :rank

  def initialize(str)
    @rank = str[0,1]
  end

  def > (other)
    #?????
  end
end
开发者_开发技巧

You might be happier if you define the spaceship operator instead of greater than. (<=>)

Sorting, for instance, depends on it being defined.

http://ruby-doc.org/ruby-1.9/classes/Enumerable.html

I would agree with darrint.

All you need do is include Comparable and define <=> and then you will be able to do all the other comparisons for free! Giving you a lot more flexibility than just defining '>' on it's own.

In the words of the pickaxe book: "The Comparable mixin can be used to add the comparison operators (<, <=, ==, >=, and >), as well as the method between?, to a class. For this to work, Comparable assumes that any class that uses it defines the operator <=>. So, as a class writer, you define the one method, <=>, include Comparable, and get six comparison functions for free."

A full example is available in the (free online) pickaxe book: http://ruby-doc.org/docs/ProgrammingRuby/html/tut_modules.html#S2 (scroll down a couple of paragraphs to 'Mixins give you a wonderfully controlled way..')

You can use the array.index method. The following code checks the index of both cards and returns true if the other card appears after the current card.

class Card
  @@RANKS = ['A', 'K', 'Q', 'J', 'T', '9', '8','7','6','5','4','3','2']
  attr_reader :rank

  def initialize(str)
    @rank = str[0,1]
  end

  def > (other)
    @@RANKS.index(other.rank) > @@RANKS.index(@rank)
  end
end

ace = Card.new 'A'
king = Card.new 'K'
nine = Card.new '9'

puts ace > king
puts ace > nine
puts nine > king