Overriding the == operator in Ruby

Question

According to the docs, Array.include? uses the == comparison on objects. I come from Java where such things are (usually) done with .equals() which is easy to override for a particular object.

How can I override == in Ruby to allow me to specify the behaviour of Array.include? for my particular object?

See also https://stackoverflow.com/questions/7156955/whats-the-difference-between-equal-eql-and — David Moles, Feb 17 '21 at 01:17

score 77 · Accepted Answer · answered Jun 25 '12 at 09:43

77

In Ruby == is just a method (with some syntax sugar on top allowing you to write foo == bar instead of foo.==(bar)) and you override == just like you would any other method:

class MyClass
  def ==(other_object)
    # return true if self is equal to other_object, false otherwise
  end
end

answered Jun 25 '12 at 09:43

sepp2k

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5

Would you need to also overwrite the hash and eql? methods? – Vitalij Jul 11 '16 at 17:00
2

@Vitalij eql? is usually just an alias for ==, and you do need to override hash if you intend to use it in hashes and sets. – bluehallu Dec 06 '16 at 17:34

score 1 · Answer 2 · edited Jul 10 '21 at 23:02

As described above, == is a method in Ruby and can be overridden. You code a custom equality condition in the method. For example:

class Person
  attr_reader :name, :gender, :social_id
  attr_accessor :age

  def initialize(name, age, gender, social_id)
    self.name = name
    self.age = age.to_i
    self.gender = gender
    self.social_id = social_id
  end

  def ==(other)
    social_id == other.social_id
  end
end

You don't need to override other methods any more.

Overriding the == operator in Ruby

2 Answers2

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