Question

Given I’ve got an array arr of instances of a custom class My_class. This class has got a couple of different instance variables. Let’s call them :name (a String), :is_processed (a Boolean) and :date (a DateTime). All of them are readable.

What is the best way of checking, whether another given instance of My_class (call it newbe) is already in the array based on the content of the aforementioned instance variables?

Using arr.include?(newbe) will not work as this compares the object IDs, doesn’t it?
Can I override the way Array#include? compares two objects?

---

Speaking in code

class My_class
  attr_reader :name, :is_processed, :date

  def initialize(_name, _proc, _d)
    @name = _name
    @is_processed = _proc
    @date = _d
  end
end

somewhere else

first = My_class.new("First", false, DateTime.new(2001,2,3,4,5,6))
second = My_class.new("Second", true, DateTime.new(2001,2,3,4,5,6))
third = My_class.new("Third", false, DateTime.new(2001,2,3,3,2,1))
newbe = My_class.new("Second", true, DateTime.new(2001,2,3,4,5,6))

arr = [first, second, third]
arr.include?(newbe)  # => false but should be true

Answer 1

You want to compare instances of you class, so include comparable, define a <=> method and you have added these methods to your class instances:

<, <=, ==, >, >=, between? (#include? uses #== ).

require 'date'
class My_class
  include Comparable
  attr_reader :name, :is_processed, :date

  def initialize(_name, _proc, _d)
    @name = _name
    @is_processed = _proc
    @date = _d
  end

  def <=>(other)
    [self.name, self.is_processed, self.date]<=>[other.name, other.is_processed, other.date]
  end
end
first = My_class.new("First", false, DateTime.new(2001,2,3,4,5,6))
second = My_class.new("Second", true, DateTime.new(2001,2,3,4,5,6))
third = My_class.new("Third", false, DateTime.new(2001,2,3,3,2,1))
newbe = My_class.new("Second", true, DateTime.new(2001,2,3,4,5,6))

arr = [first, second, third]
p arr.include?(newbe)  # => true
#you could do arr.sort, but they are sorted allready by accident...